We 3 partners entertained assembling the structure (we build airplanes, right?) but the local city required a licensed contractor and we all had day jobs and winter was close and another hangar was just completed and that builder offered us a sweet deal cause the crane and crew were already on site, etc. So we did the smart thing and let the pros assemble the hangar.
An important item I listed above was the asphalt pad. We built on the last lot at the end of a row so we had to bear the cost of the pad in front of the hangar. The city inspector also stated the city's position, "No pad - no occupancy certificate." Your local rules may be different.