I agree after seeing the plans versus what's built that you have a very clear suit against the builder. Everything that's been said about chances of recovering more than attorney fees applies of course.
The original design is pretty good, as a concept. The columns aren't "paired", they are trusses. The side carport structure or whatever it is (that appears to have been dropped off the actual built structure) creates a strong braced frame to provide lateral wind resistance. I would have preferred a bit more lateral wind resistant design perpendicular to the gable end walls, but other than that I think it's a good design.
Are you telling us everything? Did you really have a design for a gabled roof building with a side garage or carport "lean to", and then accept the contractor building a flat roof box with no side garage instead? Or did they suggest maybe this would work better and you agreed? A lot of those "side conversations" or agreements will come into play in any legal actions and remediations.
The problem with adapting what you have is you're going to have to break down the space into pretty small pieces to work from within, or put in some very hefty moment resisting frames to hold up the existing built structure. Moment resisting frames can require a lot of foundation, and are going to eat up a lot of internal headroom and some floor space.
Your structural engineers fix will dictate what is feasible, and what it will cost. I'd take that to the contractor, not come in with a suggestion that they put a wall down the middle and start doubling up columns. Putting a wall down the middle and doubling columns won't get you anywhere near the original design, might not be structurally sound still, and will not accomplish what you started out to get and paid (at least partially) for the first time. You come in and ask for and agree to a substandard correction before you even have an opinion on what a correct solution is, and in a few months you'll be posting another thread about what to do next because your building still doesn't work. And, you'll be in even poorer legal position, because the company will have done what you asked for, and you are still not satisfied. The best is to ask that you be put into the position you originally contracted for.
It very well may be least expensive to dismantle this and start over, unless you're willing to accept a very different product than you wanted. For instance, you might be able to make a pretty good house out of this, with a small internal garage or shop workspace. Or a series of smaller shop rooms and one or two small garage bays.
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