I'm planning a playhouse for my kids based on an airplane called the Sea Duck. I have a rough plan made here and am using plans I bought for a playhouse on stilts as a structual guide. The structure will be about 11' long and 6' from floor to ceiling. It will use five 4X4 posts as stilts and they will go to the ceiling of the fort. The floor and wall cladding will be planks of 1X6. It will also need a pitched roof but I didn't show that in my rough plans here.
Any tips or advice from people that have worked on similar projects? I want to make sure its going to be safe and sound for my kids and will last a long time. I could really use some advice on leveling, draining, and building the foundation for the posts. Such as how deep do I bury them and how much concrete should I anchor them with?