I live in KY in the summer and have a steel building with shed roof extensions, one to house the RV. 6 x 6 posts, ten feet apart, 2 x 6s between the posts, prebuilt rafters 5 feet apart, corrugated steel for the roof and walls. They go up quite fast and if built right they are strong enough to withstand heavy winds. The floor is poured around the posts, but you could cut out large areas of the concrete where the posts (three feet deep) will be located and then pour concrete around the posts out to the original concrete.