Hey janvit, i'm just in the middle of making a grow tent at the moment, you can buy purpose built ones online, but they're between £100 and £200 pounds so i decided to make my own. I went to a gardening centre and bought a normal outdoor plastic covered growhouse for £20 then went to my local hydroponic shop and bought some light proof sheeting for £5. The grow house is metal tubes that just slot together, so i simply assembled it and cut the sheeting to size and taped it on with insutlation tape. it's got shelves but i only put the top and bottom ones in, the top one to hold a fan and suspend the light from and the bottom one to put the plants on. It's 2' by 1 1/2' by about 5' high. Only small but it'll fit 3 plants in which is all i want. I'm sure you can get bigger grow houses tho if your planning on growing more plants. A 250w hps won't be strong enough for an area of 1m x 2m. 50w per sq foot is what you should be aiming for. For 1m x2m you'll need a 1000w hps. (Rough conversion of metres to feet in my head 3x6=18sq ft 18 x 50=900) A 250w hps would only be good for an area of around 5 sq ft. (2.5 x 2 ft =5 sq ft)
Quick conversion to metric 0.8m x 0.6m ish!