From what you describe, there is a 40 x 72 pole construction shelter, no walls, wood posts holding up wood trusses with a steel roof. The last pole building I costed out (54 x 60) with a local Co-Op and verified with M&S was around $10/SF plus about $2.50 for concrete floor. This had wood 6 x 6 posts, wood engineered trusses, steel sides and roof, 2 16 x 16 sliding doors, and a service door, no elec. or plumbing. Maybe I'm not reading your description correctly but I'd think $10/SF should more than cover it. Maybe its a locational variance but in this area, you can get a 60 x 120 indoor riding arena for about $8/SF base cost of the steel building with roof,walls, and a few sliding doors. Steel has recently shot up so these costs may have changed in the last couple of months.