A detached structure gives you more freedom to have what you want without having to fit into connecting to a current building and being influenced by materials etc. Also, it is easier to build a free-standing structure than attaching to a house. If you wanted a room over your garage, as a detached, free-standing building this would be easier.
Depending on the use of the garage and what amenities you wish to have in it. Generally drainage but if you want electric or water this needs to be considered. When doing the groundworks for the garage, the ground it sits on to how much groundworks is necessary, also the location of the building if it is easily accessible or not.
For a non-habitable outbuilding, no building regs are necessary.
Additional planning info here
We have a range of single storey garages and room over garages, these are based on the best bay size to accommodate all ranges of cars (based on a Land Rover Discovery) to fit in. If it is possible to use a standard design template this will save you money on design time and structural calculations. If you have a specific design you wish, this is not a problem and you do not need to employ an architect, we can design the building you want to suit your needs and your plot.
Garages with room overs are very popular, a place to store the F&F’s (Friends and Family) when they come and stay above the garage and workshop hits 2 birds with 1 stone. Aesthetically more people are requesting roller shutter doors, functionally car collectors and hobbyists are putting car lifts into their garage to be able to tweak at home.
Yes if it is on the plans and will be zero-rated (if it is a new build)
Depending on the size of the garage depends on Permitted Development. A couple of general rules apply: Behind the front elevation of the house, Under 4m to the ridge (Top of the building), No more than half the area of land around the "original house" would be covered by additions or other buildings, further than 2m from a boundary (any closer limits the size of the building again).
An erected single story 2 bay Country Buildings oak garage starts at £8,000 inc VAT, a 2 Bay Room over timber garage is £22,700 inc VAT.