I have 7 raised grow out beds for bonsai. They start out from the bottom with 1/4 inch hardware cloth to keep rodents from tunneling in, with next layer up being fabric weed block to help control roots, keeping roots in and out. All of the grow beds are 2 x 8 inch pt wood, Other beds I have are up to 12 inches that hold mulch for heeling pots in. Some of my beds use coco choir and some have a mix of a peat / perlite mix amended with pine bark. My oldest bed is just topsoil and another larger bed is topsoil amended with pine bark, compost, granite and everything else I had on hand. All of my beds are growing trees very well, and I understand fully well the importance of a well aerated mix, but the amended soil and the soil beds are giving me a lot more growth. All of my beds have a homogeneous mix, and none of these beds are layered.
I would caution against a layer of grass clippings as they will pack down and become an anaerobic sloppy stinky slime. If you use grass you need to use thin layers alternating or mixed (better yet) with mulch, chopped leaves or another source of carbon. On occasions where I have a deep growing pot of bed that I need to fill, I use pine bark for the bottom layer.
There is a hundred ways to do a raised bed that work and a hundred ways that don't. Most of it common sense based on experience and observation.