I'd actually build a room inside a room so I would just build a flower and veg room within that room with 2x2s and panda film, but most would just split the room. To do this all you need to do is build a 8 foot frame however high your ceiling is with 2x2s or 1x3s. Either put some money into it and nail up some plywood to the frame or just staple panda and/or poly to split room for darkness in flower. Create a door to flower room with stick zippers or velcro, or if putting up plywood just make a door from the plywood and add a few hinges. Key it to have total darkness of which I'm sure you already know.
Use the remaining half of room to create another split(another frame) for your veg room, and then you have the room closest to the entering door for the needed extra space.
It would be so much easier to draw it out then explain it.