Step 1: Figure Out The Size
Step 2: Materials
1. One or two pieces of plastic big enough to cut the windows out of.
2. Enough 1x3 board to go around the edge of the window size.
3. Threaded rod and nuts (used 1/4-20 in this model)
4. GE Silicone Door and Window caulk to seal around windows
5. Building stuff skills
Total cost was $10 for plastic, $2 for wood, $2 for hardware and $3 for caulk.
And you will probably need for tools:
1. Saw to cut windows to size if they are wrong size
2. Saw to cut wood boards to size
3. Drill to drill holes in the top for threaded rods.
4. Method of putting the appropriate groove in the boards (see step 5)
Picture shows necessary building stuff skills for this project. (just kidding)