One thing to consider is engineering plans. The company I got my RV Port from provided engineering plans for FREE. One outfit I called wanted several hundred dollars for the plans. Why did I need this? I live in the city limits and a building permit is required for the structure prmiarily for "Wind requirement 110mph rating" When submitting the plans, the engineering plans needed to be attached. Can you get by without a permit?, maybe if you live out in the country but in my case, funny story was that the building inspector said "I look at your house every day with my morning coffee" Seems she lives near by!
I priced stick built shops for the RV Port but could not joke down the cost. But when I had the foundation poured I had it made as if I was going to build a stick built shop so if I ever change my mind in the future the slab is ready...