Agreed.
Good idea about the side door.
27x48 is a bit small, depending on how many chicks and how long they stay in there.
Also, consideration for how well something like a brooder plate will fit in there would be a good idea. My plate is 18.9 in. x 12 in. so it would fit, but a little...
Looks nice.
I would omit the divider, I don't see how that could be split into 2 brooders, each section would be too small for food/water and heat.
What is in the bottom? A particle type board? That may come apart with moisture over time. Coroplast in the bottom would be quite slippery...