Have you considered getting a motorbike shed instead?
A lot cheaper, doesn't require planning permission, dodgy builders or the like and will give you enough room for the bike, tools & space to work on it.
Plenty of different size ones available too.
Link: http://www.ebay.co.uk/itm/Metal-Motorbike-storage-Motorcycle-garage-Secure-Motorbike-Shed-/170809377479
Link: http://www.brodco.co.uk/daylightsecure/motorbike-storage/
Link: http://www.trimetals.co.uk/product/motorcycle-garage