Things You'll Need
Instructions
Design the door. This can be as simple as using a sheet of plywood or a fence gate and as complicated as building a small version of a door for a house.
Assemble the door and use a drill to screw the hinges to it according to their instructions. Lay the door inside the trim with the hinges facing up and screw them to the trim. Lay a piece of scrap wood over the door and the frame, and hammer a nail through the scrap wood into the frame at each end. This keeps the door from flapping open and closed while installing the door.
Hold the door frame inside the rough doorway in the playhouse so that the door opens in. Nail the trim to one side of the door frame, and use more scrap pieces of wood to fill in the gap on the other side. Nail the scrap pieces of wood to the other side of the hole and the trim on the door frame.
Remove the scrap wood from the frame and test the door.