I'm not sure who needs to hear this but, until this year I had always wanted to make DIY cinderblock ledges but never did because I could never figure out how to get the measurements for angle iron to line up with the exact length of however many cinderblocks I wanted to make the ledges out of.
Some people will say "just cut a bed frame" or whatever but I've never been very good with power tools and was never taught how to properly cut metal or anything so that approach never worked.
For some reason, I never considered the idea of checking with local metal shops to see if they could make custom metal but I got recommended that by a friend and it was so easy and cheap. So if you ever find yourself in a similar predicament, here is how to do it.
Call a local metal shop. Ask to see if they will make you custom-sized metal. Ask if they can make 2'x2'x1/8 pieces of angle iron and if they can just ask for it for the length you need (your average cinderblock is 16in long). It is mad cheap too. A 6ft piece is like $4 at my local shop.
I've built three different ledge spots this year and my local scene is benefiting from it. Hoping this information will help you and your scene as well.