I'd like to try to make a window perch for my cats. I'm not very happy
with the ones I've seen sold in stores. What I'd like is to have a
window perch that doesn't have to be screwed, nailed, or glued to the
wall or window sill. It should also be able to hold at least 20
pounds.

I was thinking of using thick particle board. Then screw on two or
three L brackets that will allow me to slip the brackets between the
window sill and the window.

After that I would need some other brackets that would go from the
bottom of the perch to the wall, for support.

I just don't know if any of this would work. Any opinions?
If particle board is something I can use, can I buy that at Home
Depot? Can I buy just the size I need (something like 24"x12") or do I
have to buy the whole sheet (or however they sell it)?