I'd say bigger. Then you can expand. To conserve light, hang a mylar curtain across the room at the right dimension for whatever light you're using. Then if you get another light, just take down the curtain. When I was in my growroom I was using 1x1000 +1x400 HPS in a space 7x12 feet. I'd say ideally make a 8x16 room, then you can divide it for veg/flower, or you can add another 1000w, and still be able to walk around and tend your girls.