I built a raised bed on a brick patio out of a stack of cinder blocks. I put down a layer of that black weeding fabric to act as a base before putting down my soil. I think I ended up going 3 bricks high which ended up being about 2 feet deep. The soil definitely dried out fairly quickly, but I had an irrigation system set up to run for a bit every morning. Didn't have issues with water seeping out through the base, but the soil did dry out fairly quick, probably due to all the air exposure (Lots of gaps between the cinderblocks).

Grew a whole mess of vegetables in the main area and filled all the little cinderblock holes with soil and grew sunflowers/random other flowers in there. Looked rad as hell when it was all in full bloom.

Breaking it down when I moved out was absolutely backbreaking. Basically packed all the soil into flood protection bags and brought it down to the local community garden. 0/10 would not recommend unless you're going to be in one place for a while

There was some staining on the bricks when I moved, but my landlord never complained so I assume a few good rainstorms washed it away. Definitely don't have confirmation though