I’m in the process of making my shed/garage type thing. I had a concrete pad laid, bought a shedload of 2×4 and a load of 8”posts. Put the posts up on galv post stands bolted to the pad, joined them all together with timber. I made some pent trusses out of the 2×4, plonked them up on top. Laid some membrane over the trusses, then some ebay bought slight second metal roofing. Clad the frame in ply, then membrane, then feather edge. I’m just working out how to do windows and doors now. It’s been a learning experience, and probably not the cheapest way to do it. But the structure is amazingly strong now, and it’s been an enjoyable process.