A metal cutting saw (dremel,,jigsaw, "scroller saw"[from 1980 like I have lol], or something of the like.
Drill with metal cutting bit, and Grindstone.
1/4" Thick Piece of acrylic.
A case :/
And strong glue. ( I used some I got at an auto show)
And a flat surface.
There are other methods, but this is what I did.
1. Pencil the shape of the window.
2. Drill A hole at the starting point.
3. Sweep away the metal shavings, NOT with hand (so acrylic isn't scratched)
4. Cut the metal along the pencil lines.
5.Using the grindstone on the drill, smooth the edges along the recently cut part.
6. Repeat step three, then move to step seven.
7. Mark, with a magic marker or something of the like, the shape of the window(remember to leave about an inch extra for gluing(sp?) space.
8. Cut the acrylic along the line.
9. Repeat step 3, then move to step 10. (nothing worse than a scratched window.)(Acrylic scratches easily)
10. Glue the recently cut acrylic to the inside of the case's side. Let it dry.
11. erase any stray pencil marks.
12. Spray the window with Windex, with a SOFT cotton cloth. Like cleaning glasses, or sunglasses.
remember, this is just what I did. Most people use bolts and such, but I wanted to keep it easy. I also picked up some Chrome car door trimming which went nicely around the window. If it is an exotic shape, you can put a big square of acrylic onto the inside, or cut smaller pieces. remember to keep it clean, you don't want to scratch it.
I just got done with mine. I used a jigsaw, big right angle ruler, magic marker, metal file to deburr the cuts, one of the wife's tupperware bowl that had a nice oval shape...hand drill , 1/8 plexiglass and nuts/bolts. Looks pretty good eh?