two places around me sell used ones and i have priced used 53 foot used for 2800-3000 delivered in my area.
as far the the top goes it seams easy enough to build tall enough to park a skoolie under without trying to do the rounded roof or if thats a must then try to find some old grain silos the width and cut it in half?
long story short the company i used to work for. on the big projects we had a set up with trusses,walls,roll up doors already fabbed and stored in the containers. when it was needed on the job we would place the containers 20 feet apart,rock in between and pull the already built trusses wall framing and cut to length and marked tin for wall panels and roof panels.
an experienced four man crew could almost build it in an 8-hour day but we got good enough that we could dismantle one move it and rebuild it in three days.
the company had seven set ups. when needed we could have full size small sheetmetal shops and pipefitting plumbing shops right on the job with storage for the equipment,fixtures,materials to installed on the job.
was always nice to have