I have a homemade wooden one my daughter has outgrown but I'm in scotland and it doesn't fold down.
It was easy to build - I built a timber frame, used OSB for the roof and floor and with cheap tongue and groove for the walls. Tiled with singles and and painted.
You should try it, it very satisfing when it is complete, and cheaper and nicer than the "sheds" from B&Q. ... or if you have a trailer and a lot of time you can have mine for £80.