I've used kiddie pools before, but the problem with them (from my point of view) is it doesn't take long for the chicks to start jumping out.
Earlier this year I found a Kiddie Koop playpen from the 1940s at a thrift store - CHEAP ($15). I thought it was a rabbit hutch until I got it home and saw the tiny Kiddie Koop logo. It has a drop down side, as shown in the picture, but what you can't see in the photo is that it also has an attached top that slides over and down to be stored on the back side. Chicks can't jump out, and I don't have to worry about my dog or cats stealing chicks from the brooder. My favorite part is that it collapses for storage, so it takes up very little space when I'm not brooding chicks.
When the chicks are young, I put them in a rubbermaid tub inside the Kiddie-Koop, to protect them from drafts. It would be easy to add plywood or plexiglass to the sides if you wanted permanent draft protection.
We just used a cardboard box. A small box when they were really little, then a recliner box from a local furniture store when they got bigger, but were still to little to go into the coop with the older hens.
If in a protected area, I use 1/4 in hardware cloth folded and cliped into what ever size is needed. Total cost the one that I built was $35 and I have enough to build 3 or 4 25in by 30in boxes. they are very easy to clean and don't take much time to build. I use mine for quail so they are relativly small. hope it helps
Watch the curbs, too! I use an old horse trough that had a major leak in it. I just put duct tape over the leak (the edges are sharp). You can find all sorts of things on curbs - I've seen several horse troughs in the country on trash day!