I am building a double garage in the spring the garage is 16,9 wide 24,7 long it is a concrete sectional garage made by compton i bought on ebay for 300 pound including garage door .I had to dismantle it and transport it probley cost me £60 to hire transit open back the leaf springs were on the on the bump stops was hard graft but did in the end so i know how to put it back up .The building regs say that it has to be 5 meters away from your house and if a base of concrete is under 30m square you wont have to have building inspector but if it is over 30 it will cost you 130 pound to the building inspector you then submit a plan or outline of how thick concrete and what reinforcing you will use he will check it deep enough then give u ok if he is satisfied ,alot of councils differ in depth but 2inches of type 2 then damp proofing 5 inches of concrette is enough .....Hope this helps so if you look about you prob pick up a good second hand garage like me ..............