Small box idea (split from growroom setup sticky)

Hey there, first timer here, and I was planning on building a small box with a 3' x 3' footprint, but I can't seem to find any information as to what the optimal height for this box would be. I was hoping to keep the height on the minimal side (maybe 3ft. ?), but I plan to run at least a 250w HPS, and I'm afraid I'm going to run into issues with temperature, and/or plants being too close to the hot lamp. Any feedback would be great appreciated! Thanks!