When living in an apartment, my darkroom also doubled as the kitchen (or bathroom). I have had permanent darkrooms in 8x8 rooms. My current darkroom is 12x12. I had two enlargers and a Jobo processor in the permanent darkrooms. Keep the dry and wet side separate--it just save a lot of headaches. And then it is just about organization. Think about the way you work and the things you need. Oddly enough, ceiling height can get you into more trouble than the width and lengths of a room--I have an Omega D5XL with the column mounted below the work surface.