Is there a standard for depth of the drain below the frame?
Typical for my area is 8" (or more) below the bottom of the rough opening of the window. Typical clear depth includes an aggregate (gravel) material of at least 4" in depth.
The width is typically 4"+, of either side of the window rough opening, and this extended depth from the foundation out of at least 12", although it is recommended greater. Hope this helps.