I'm not sure what the overall dimensions of yours are. I can see the 2' width and an overall height of 3 feet, but that is it. I also cannot tell what you have as a floor. Is it plywood or hardware cloth?
I'll show you what I did to raise them in the coop. I've raised as many as 28 chicks to age 4-1/2 weeks in it. It is 3' x 5' and 24" tall. The floor is one piece of 1/2" hardware cloth. The sides and top are 1" hardware cloth. I took a roll of 2' wide hardware cloth and bent it to form the sides and used J-Clips to put it together, them put a piece of hardware cloth on top, again connecting it with J-Clips. To make the doors, I cut out a hole, one in the front and one on top. Then I cut an oversized piece of hardware cloth and using J-Clips as hinges, put that on. I use a snap lock to hold the doors closed.
To get it in and out of my coop door, I had to build the frame separate. It is basically two H-shaped sections with a couple of bottom railings to connect them. The brooder sets inside that. Then I used a piece of plastic all the way to the ground to make a draft guard.
The reason I have that plywood thing on top is to make a "chimney" to put my heat lamp so the other chickens in the coop stay out of it. That was not a problem with my first chicks but it was after I had other chicks in the coop. In your shop, that would not be a problem for you. That duct tape on the top right corner is to cover up the sharp edges so I don't snag my clothes as I walk by. That corner is a tight squeeze by my nesting boxes.
A couple of problems with mine. The wire floor is not real level and it bounces when they walk, especially when they get a little bigger. I had to fix a piece of plywood to the frame and level it to set the water on so they don't spill it. My only access is a door in the front. I can't reach them in the back corners to catch them, so I made a small net out of a piece or bent wire and a net onion bag so I could catch them. Any spilled feed goes right through the floor so it is lost.
The poop falls right through the 1/2" hardware cloth floor. If they drop a chunk too big to go through, their walking on it after it dries a bit pushes it on through. So expect a real mess underneath. It's really not that hard to rake out for me, but in your shop it might be a problem. Maybe make a tray and put bedding in that to absorb it and make something easy to clean out?
I'm not telling you to build one like mine, more of showing what I did and point out a few problems so maybe you can avoid some of them.
As to yours, how do you plan to clean it out? The only access I see is through the top. That top door will be handy in catching them and providing access to the feeder and waterer, but you might want to consider a side door for cleanout.
I like your use of hardwire cloth for light and ventilation. My theory is to heat one area to the right temperature and let the rest of the brooder cool off as it will. Usually that is 20 to 30 degrees cooler than the recommended temperatures. That way they can find their own comfort zone and you don't have to worry about keeping the whole thing the "right" temperature. I think you achieve that.
What I might suggest is use the plywood to make a "draft guard" about a foot high and make the rest of the sides out of hardware cloth. I know it is to be in your shop, but I like the idea of the brooder not depending on location to keep the draft off. Maybe you want to leave a door or some windows to the shop open? Or make your sides 100% hardware cloth and plan on attaching something as a draft guard, especially if the bottom of yours is hardware cloth. I know hardware cloth is expensive, but maybe you don't need any plywood at all, depending on how you do your floor.
I'm guessing that yours is planned to be 2' x 4'. That size might work out for 25 chicks at 3 weeks age, but I'd suggest looking at making it bigger. I think it is going to get pretty crowded as fast as they grow. That just seems too small for 25. If you make it a little bigger than the minimum you need, you have a little flexibility in how you manage them. Something may happen that your three weeks in the brooder becomes four.
Instead of using 2x4's, I'd suggest ripping a 2x4 to create 2x2's. You get twice as much length, 2x4's are usually less warped than the 2x2's you can buy, and here a 2x4 is a little cheaper than a badly warped 2x2. Those 2x2's will be plenty strong enough for what you want to do.
You can do your heat lamp like that, just setting it on top of the wire and keeping a steady heat to the one area, provided your brooder is big enough and well ventilated enough for the chicks to get away if it is too hot. I don't know if the ventilate part is a problem in your shop. You could change the wattage of the bulb or hang it and raise it to cool off if you need to. But in any case, I suggest securely attaching the heat lamp where it cannot possibly get knocked off or fall. Do not depend on the clamp that comes with it. Use wire or something really secure. That secure wire will do more to lessen the fire hazard than anything else.
It takes up a lot of room, but if I had to do it over again, I'd build something permanent in the coop. Put it a foot or two off the floor so I can clean under it, and make it almost entirely out of hardware cloth and those ripped 2x2's. It would not be that hard. The biggest problem I see is figuring out how to provide heat that is secure from the other chickens and that is not that hard to overcome. It is just something you have to think about ahead of time. This way, I could raise them with the rest of the flock from Day 1 which I think helps with integration. I keep all chicken supplies in one place and I keep all chicken smells and dust in one place. With it built in with a wire floor, I have a broody buster and a place to isolate an injured chicken while keeping it with the flock. It would not work as a quarantine area, but if you wanted to integrate a few chickens later on, you could keep them in here to get them used to the flock. And I would build a solid, level area for the waterer. That is a pain with my current one.
I know my situation is different from yours, but maybe you can pick up something from this that helps. Good luck!
