What style are you using SOG? With 4ft high you have limited high and with a 125w!!! Ok here's what i'd do is go with 4X4X6 and for the roof i'd use clear poly, line the inside with some mylar or white poly go with a SOG soil bed set up and veg to 10"-12" depend on strian. I'd use CFL to veg and then just use mother nature to flower. When you are vegging just keep the black poly on the top. The only draw back is you have to manually cover it at nights and take it off in the morning for flowering. If you do 25 plants in there you can probly pull 3/4 lbs if done right. With lights you are back to gram per watt max you'll be lucky if you pull 50grams from a 125w light. Thats what i'd do, hope that helped give you some idea's