Need plans/design for window perch

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)?
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On Sat, 23 Jun 2007 06:34:26 -0700, "Mike S."

Not sure, but isn't plywood stronger for the same weight? I think it takes screws better too. And resists water 100 times better.
I thought particle board was used because it was cheap, just like Steakum's, which they refer to as flaked, chopped, and pressed, but what they really mean is "the stuff we scrape off the tray after we cut the good meat."

Not yet.

I think they sometiems have partial sheets in the back. Actuallyl, they or Lowes said that about sheet rock. Not sure if it applies to other things. There is more than HD. A lumber yard may cut a piece you need.
What kind of windows, window frames, and window sills do you have? What kind of walls? A lot of ways to do this type of thing, the more thinking in advance the better.
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Mike S. wrote:

http://www.futurepets.com/Cat_Window_Perch.htm
http://www.kittyview.com/home.html
http://www.instructables.com/id/E5DZ1ITGRGEP286YQ0 /
http://www.bizrate.com/catsupplies/products__keyword--cat+window+perch.html
plus 460,000 Google hits for "cat+window+perch"
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