Here is an idea to look at.
A friend and I actually built a small backyard shed using the above idea. Kind of like playing with a giant Lincoln Log set. He was in rent house, and wanted something that he could use and move when he moved. Used 8 foot treated lumber, gave him about 7x7 inside dimensions. Now that he has bought a house, it has turned into his granddaughters playhouse. .

That forum has some pretty good and what I call crazy ideas that will work. Well worth spending some time getting ideas.
"Infantryman, the ultimate hunter, where the prey shoots back."
"Illegitimus non carborundum est"
"Real friends don't let friends use electronic calls"