Thanks again. Looks like i'll be getting a rhino after all then, I've got a few weeks before flower stage to save up, and the seedlings are currently in an inside grow using 2x22w CFL blue bulbs with an ordinary desk fan to circulate the air.
The outside room was built by a previous owner and has it's own fuse box and 6 x double plug sockets. Seemed rude not to take advantage of it!! The building itself is timber but was used as a workshop for repairing antique watches and is boarded out like any room in a house, and has 3" of foam board insulation all round.
I've seperated a section about 3'6" by 8', and only now plan for a small grow at one end, which i might seperate using foam insulation board on 2 sides. Currently the inner room is made up of spare chipboard, with an external layer made of swimming pool cover, which absorbs heat and doesn't let it back out. I will be using a 125w CFL to grow flower 4 plants, 2 harvested every month. I also have some home made reflectors using cooking trays that I bought for 50p each (60cent), with each having 2 x 20watt cfl's pushing out about 1450 lumens each, to even the light out.
There is currently a 4" whole cut in the outside of the building, with tight cloth bug screen, on my first grow from cuttings this seemed to help keep the air a little fresher and cooler, but obviously not much.
Oh and due to regular hoovering, disinfecting all surfaces, and leaving shoes outside, combined with every join on every wall, ceiling and window being sealed with silicone, I managed to have a grow bug free