Step 1: Gather needed items
2-Mesh or Screen--for bottom of tray, something permeable, but that seed won't fall through
3-1/2" or 3/4" piece of wood the same length of the longest side of the frame you chose
4-L-shaped fastener with screws
5-Long nails or Screws, a hammer, and a drill if you have one
Screw the L-shaped fastener onto the wood plank as pictured, so that it will latch over the lip of the window sill. Screw another one to the other side of the wood plank.