I worked in Alabama for a year. Spent a little time in MS too. Things are done differently there from what I'm used to in CA. Yes, we are over governed AFA construction goes. OTOH, in places I worked outside of any AHJ in AL anything could and was expected. A complete circus from my standpoint.
So, we don't know where you live and who has what authority. What's more, we don't know if your contractor is even
required to be licensed. Before you do anything, you might look into what little leverage you may have. If your contractor has little to few assets, then suing him won't do much but cost you time and money. IOW, no gain and likely a loss.
Depending on the answers to the questions I posed, hiring this expert and that lawyer might be far more trouble than what that building is actually worth.
I am NOT saying it can't be corrected and saved. What I'm saying is that you need to find out a LOT more on your own. You've already made some big mistakes so try not to make any more. Knowledge is power but you don't always have to pay for it.
This post makes the most sense to me:
I have seen a lot of build threads with these sort of buildings. I usually stay on the sidelines.
If you are finishing out the space - starting with a carport is penny wise and pound foolish. I said something similar on question about a pole building as well. Now I am sure that someone out there is building a metal building from all this light gage material that might actually build a good building.... I just haven't seen it yet.
We all know accessory buildings (Shop, garage, mancave..... whatever you call it) don't add value to resale. So I completely understand desire to not go over the top unless you have a bunch of money, never plan to sell, are using the space to make money, or have other requirements (like zoning/HOA) that force some of these fundamental type questions. If you are looking mostly for dry storage I can see these sort of buildings fitting the need.
I also get having a job in another area of expertise, building a building is a skill and also a good chunk of time that most of us don't really have to do. So getting a quick shell up and then being able to chip away at things inside at DIY pace that allows life to happen - there is a logic to that. The important part is to know what you want at the end then take steps over 6mo or 10yrs to get there. If you are going into this as a known temporary thing then a 5-10yr effective life is reasonable, just don't think it will be the same as a structure designed for 50yrs.
As for this building- not knowing what the foundation is makes it really hard for me to even say if you really can come out ahead with a rework plan. The trusses look very light and even appear to have a sag to them already. The good news is that you appear to be building a building inside of it to finish it off, adding some structure and connecting the two might save your day but it will probably involve adding some beams/trusses and posts at the ends to make it all work.
My $0.02 (which I am way past) is at the root of this is there was not a clear matching of expectations between owner and builder at the start of the project. I doubt that if there was this would have been the builder you would have chosen.