If more photos of the build were included, this would be more helpful. Also, it would just be nice to see the brooder in use along with information about how you found its functionality after using it!
I really like the bi-fold lid. However when/if you decide to have 2 different sets of chicks ( one on each side) the bi-fold may be a problem if you only want to access the far side.
I would suggest putting linoleum or something similar on the floor to make clean up easier, and/or make the bottom removable.
Also, some people have argued for putting a window of sorts for the chicks to see out the side instead of only seeing large things coming at them from above.
