My suggestions: 1) Don't use weed blocker, put 2 layer of carbon board under raised bed, they will smother the grass under. 2) Don't use garden soil, it's going to be expensive. A 4x8 bed will require 1 cubic yard soil, that's 27 bags. Go local compost facility to buy compost in bulk. If you like, make some soil mix by yourself (google to find receipt).