grow space question

i am making a new grow box out of ply wood and have a question about how i should make this box i have only 50 inches of space in height so should i make the box 24x25x50 inches with the lamp inside on raiseable hooks with the top closed off or make the box 24x25x36 and have the lamp hanging from the ceiling onto the plant which will be seperated by plexiglass keep in mind this box will be placed in an attic so i want the safest possible way for ventilation and cultivation.

i will be adding fans to both boxes either way

You would need thermostatically controlled heat in there too... I would use the full height, insulate with foam sheet insulation, and rig a small ceramic heater in there.