Are we talking about draining water away from the garage?
Perforated, black plastic, 4 inch pipe is sold in 20 foot and 100 foot roils.
You will want to get the fabric “sock” that goes over it to keep any fine dirt from getting in and clogging it.
You will want at least 6 inches of gravel all around the pipe, Top, bottom, and both sides.
12 inches is better.
Line the trench with the black fabric before putting in any gravel. Have enough fabric on the side to be able to cover the top of the trench. Then you can sod over it.
Gravel should be washed. No fine stuff. And about the size of a chicken egg. (I have forgotten the size number.)
