Step 1: Materials and tools
Materials were principally two large plywood packing crates, plus I extracted some rough-sawn planks from a heavy-duty pallet. I had a few 2x4s and some 2x2 cedar leftover from a deck rebuild. I also bought a roll of building paper and enough cedar shakes to cover the roof for the playhouse. We used a carpet offcut and some paint and polyurethane for finishing, plus some fence hardware (hinges and latches). Overall cost for the two forts was about $50.
Step 2: Playhouse
A porch, curtains, carpeting and furniture were later additions.