Here's a Cubby House built for under $30, it took 3 weekends and used a lot of scrap building materials and pallets from the local truck dealership - large engine pallets for the base and wall cladding. Old paint from the local paint shop being out of date and being thrown out about $20 cost and dumpster diving on new building sites (with the builder's permission) for scrap roofing and wall frame timber.
The cubby's dimensions are:- 9 feet long (2700mm), almost 6 feet wide (1830mm), 5 feet (1520mm) clearance from the deck to the underside of the verandah roof.
The door is 4 feet 6" high (1372mm) x 16 inches wide (406mm). The top of the gable roof is around 9 feet high (2700mm) and 3 windows are 28" (711mm) high x 18" (457mm) wide, 2 open as awning windows = hinged at the top and 1 opens at the side.
it has an inside clearance height of 6 feet (1830mm) at the walls and almost 9 feet (2700mm) in the middle of the room.
The platform was 2 long engine pallets, walls were 3 shorter pallets cut down to leave room for a porch, Four 4"x2" (100mmx50mm) posts formed the wall and roof supports. Flooring was scrap plywood, painted with ceiling paint for protection.
Wall cladding installed - old plywood veneer painted with ceiling paint as a sealer prior to final painting. Windows were custom made from pallet boards and glazed with old perspex from the local sign-writers scrap bin ($5). Window hinges $2 from a yard sale.
See it's easy anyone can do it.