Dont go to a 'hangar builder', just use any old steel shed constructor - agricultural type, grain store, that kind of thing, but carefully select the right type of hangar doors to suit the intended use. Hangar doors and their support/construction is the most expensive bit. If it's to be heated, it will simply be clad with insulated panels that meet latest building regs. For heating, use Ambirad radient heating, gas fuelled. Stanchion support ring beam and the concrete floor/slab and final finish are big considerations in terms of spec, bearing strength. Can leave dust-free powerfloated finish on concrete or use a multitude of different coatings with huge cost variations. Don't paint floor until many many months after concrete has dried, cured, but if used before then, you'lhave to blast surface to remove any trace of deposits, oil, fule etc.
Doors the single biggest consideration and critical.