I had a small available space in an out building that the Mrs uses as a utility room (where the tent used to live. I also had plenty of material kicking around from a recent loft conversion (but if I had to calculate how much it cost to build I would say less than £200 - cheaper than a decent similar sized tent).
It's fairly compact but ideal for my use - 1M wide, 1.4M long and 2.4 M high - loads of headroom, what a luxury after the old grow tent.
Knocked it up out of 3 x 2 and used foil backed plasterboard (to withstand the moisture and provide a reflective surface for the interior) and sandwiched some space blanket between the plasterboard for insulation. The floor is concrete but I have cut a pallet down to the right size to stand the pots on (again insulated it with space blanket) and fitted some casters so I can quickly slide the plants in & out for watering etc and also to give me quick access to the room.
Wired plenty of sockets (all high up) to power the lamps (a 600W Mantis HPS & a 400W MH), heater, inlet & exhaust fans, plus some spare in case I want to plug anything else in. I also plumbed in an irrigation pipe whilst I was at it in case I go away but it's not connected to anything yet.
Next to the grow room is a tumble dryer and I have vented the exhaust fan into the tumble dryer exhaust (fitted a back draft shutter of the tumble so the clothes won't smell of green in case me CF fails) and then this is vented out through the wall (if a heat signature is picked up I can explain it was the tumble - also the boiler vents out nearby so another excuse for heat) . The Mrs is so impressed with my handywork she wants me to knock up a similar structure for storage - the bonus is my structure now won't look out of place
With all lamps and fans on everything is whisper quiet.
This post has been edited by Chilli: 18 March 2010 - 12:42 PM