Sorry if this sounds rude, but you should really hire an architect before moving forward, or at least spend a good few hundred hours studying on your own. Aesthetics are pretty important, especially in a home. There are good reasons why house floor plans tend to have a lot of similarity, and that's because we humans live in them. If you built that building as laid out, you're going to hatte it. There is nothing wrong with trying to design your own building, but start from an established baseline like an American 4-square and modify it.

Shipping container homes have become quite popular. Although I don't know how they ship them.

Will second the shipping containers. Is the first thing that came to mind, when seeing your plans. Your dimensions might not line up with shipping containers, but the look does. Do need an engineer/architect for design sign off, but they save a lot on external building.

It is impossible that you will receive suitable help here to end up with a legal and buildable design for your house. There is no option here but to have the work done by licenced professionals. There are too many questions here to begin with, and the last one is really the only relevant one, making this effectively a shopping question (ie: where do I find a good architect or engineer?), so I think this is entirely off-topic.

Your design is, essentially, a Southern shotgun-style house. One long corridor down the side with rooms opening off of it. Many, many 1,000s of them have been built, and if you do some searching, you'll find loads of images. I'd suggest you even take the virtual walk-throughs of some that are available to be sure you'll like how they're laid out.

"Wood construction is standard" might be true where you live but it is certainly not true everywhere. Aside from centuries-old historical buildings that have survived, you won't find many in the UK or most of Europe, for example, simply because all the forests had already been felled for timber centuries ago. (And if somebody wants to claim that transporting trees 1000 miles to build houses is somehow "eco-friendly" they are entitled to their opinion IMO.)

"anti-water capabilities" Not all steel meets this requirement. In my old house I had to have steel lintels replaced because they delaminated, swelled, and cracked the mortar on the adjacent brick run. When I saw them after they were removed, they looked like they had been at the bottom of the sea for decades.

@alephzero It's not really relevant, though, unless you mean to have OP import British building materials and engineers and to build to British standards (which are woefully inadequate for very hot, humid, windy, or cold climates).

Steel rusts really easily from exposure. If rust could be an issue, nobody will buy it if you ever want to sell. It also gathers condensation really easily ANYWHERE as its a good heat conductor. If you do anything steel, make sure (1) you get professional advice on how to protect it from moisture and interstitial (hidden/interfloor) condensation, (2) design it to ensure the structural steel can be easily inspected any time, any part, (3) have a professional with insurance do it. This is NOT easy to do, it probably WILL need a structural waterproofing specialist or structural engineer.

@J... also Masonry construction that can pass US Earthquake, Hurricane, and Tornado codes is a lot more expensive than wooden framed buildings are here.

@Stilez re: steel rusting -- that is a serious issue for unprotected structural steel, which is why JimmyJames' lintels went bad on them (I'd recommend reinforced brick lintels instead of straight steel for their situation), but cold-formed structural steel members are galvanized (G60 to G90) at the factory, providing them with longevity easily comparable to a wood stud.

@J... -- you're pretty dead wrong here -- AISI S230 prescriptive design is permitted under the IRC in R603 (which also contains a simplified version of the AISI S230 prescriptive design method, sufficient for most DIY needs in its own right)

@FreeMan: Not really. The defining elements of shotgun houses was their incredible width constraint, often narrower than 12 feet wide, this plan is almost double that. With such a narrow width, those houses didn't sacrifice that valuable width for hallways along the side, the rooms led one right into the other. While the OPs proposed plan is a bit on the narrow side, it it still wide enough to benefit from more traditional, more livable layout approaches than "hospital room hallway". If you don't have that constraint, it's not a shotgun house, it's just poor design.

Gavlanised isnt always enough. Depends on their situation. Corrosive groundwater, inadequate concrete cover if covered, accidental removal/scratching in an area, sulfur in the air, or passage of time. Galvanised steel isnt immune, just better protected, and an advised buyer who knows its a DIY design and job will correctly know the risk is higher than usual of any mistake. Moisture is totally unforgiving, zinc eventually fails if not itself fully and sufficiently protected, and I fear you may have a trait of overconfidence about this aspect.

On a side, code here is 3 coats of bituminous paint over any zinc coating, where there is exposure to moisture, plus something physical as a barrier, to prevent the coats being accidentally damaged by anyone or anything, thereafter. That could help.

@ThreePhaseEel Of course it's perfectly possible to design a residential steel structure. OP does not appear, however, to have the required experience to accomplish that goal successfully without professional help. The number and nature of questions in their post demonstrates this pretty clearly, I think.

BSD- you're receiving a lot of negative feedback on your idea. Don't take it personally! There's nothing wrong with being creative and thinking outside the box (heck, people have turned old aircraft fuselages into houses), but there are often issues that you may not have thought about when you started thinking outside the box. Despite some of the ferocity of the feedback, do take it into consideration when you assess your abilities to design and your willingness to pay for your dream house.

@ThreePhaseEel I'm not sure you mean by "straight steel". These were angle irons just like what any normal brick facade in the US would have i.e. the bricks had to come out. It was built in the 60s and I can see a lot of houses in the area built around the same time with the same issues. Bad/cheap steel is what the mason told me.

@JimmyJames -- I'm referring to an unprotected (bare) steel part (such as an angle iron)

To build with metal (not the purchase price) is cost prohibitively infeasible as structural members, no matter what lumber prices are. For a 20' span you use LVLs, unless you really want to save a few inches on height using an I-beam.

@Mazura -- for traditional I-beam/K-joist, sure, but CFS?

@ThreePhaseEel Same approach used on my current home which built in the late 30s. No such issues.

@JimmyJames -- interesting, I wonder what your current house does differently for water management then

Oh so many comments. Thank you all. Some of the top issues: This house is not being designed for resale. It's being designed for my family to age out. I will have all my teenagers gone in a few more years and have a mother in law come to live with us. The grandparent suite on the far end is for privacy and distance. The top floor will be for visiting adult children. We will mostly live in the master suite and bath between the great room and kitchen. So, yes, we could make something more generally appealing, but it's perfect for our needs.

@ThreePhaseEel and others, a lot of you are centering on the question of how I can use steel or if it can use it at all. Thank you. That is the heart of my question. I'm more than happy to have an engineer and/or architect finish the plans. Asking one about the plans is what prompted this question in the first place. All the back and forth here is definitely helping me out. I am planning on cold formed steel. I was looking at steel joists and I would love to use k-joists, but I'm not sure they are compatible. That question was what took me to the engineer in the first place.

@FreeMan and I appreciate both ends of the spectrum. I'm not daunted by any of this.

Several people mentioned shipping containers. I'll admit that my original concept was based on that option. Then i looked at turning a shed into a house, but we have been adding rooms and other capabilities into the house.

@ThreePhaseEel Nothing different. The house with no issues has actually had more issues i.e. ice dams.

I think you'll find there are such tables out there; they just happen to be more common in ship-building and aviation.