I can't take responsibility for your installation, theft, break ins, and your A/C falling out of your window.
Step 1: Materials required:
1/4" Rubber Foam Weatherstrip
Window screen frame
Plexiglass - Home Depot
Screws, self drilling, 1/4"
C-channel Aluminum pieces 3/8' and 1/2' sold in 8' length
Silicone - Home Depot
Nut Rod Coupling and a screw that fits.