To help you a bit, we built a conservatory this summer. It's 5.3m x 3.6m (pretty big). For a laugh we asked for a quote from Everest; �15500. Way too expensive. BTW, get as big a one as you can; the quote for one half the size was only �1000 less. So, we dug the footings, poured the concrete, got a mate to do the dwarf walls (we bought the bricks), did the concrete slab. A mate of ours works for a window manufacturer, so we got the glasswork etc at trade price including replacing the existing patio door with a french door. It was also tiled, furnished and had electrics put in. Total cost �8500. If you can do a lot of it yourself, you can save ����'s. Also left the brickwork natural inside, saves on plaster and decorating. It is great. I think if you want a spare bedroom your best bet would be to convert, say, the dining room and use the conservatory as a dining room. According to all the furnishing brochures we got, loads of people do. Also, don't forget to check/inform for planning permission, advise your mortgage lender and check the deeds to see if there is a restrictive covenant which means you have to get the developers permission (this at a price, but normally only on newish houses).