In reply to crisp:
Check your planning regulations with regards to height of garden buildings... Personally I would go with apex (I did for my workshop) as it allows more storage options in the roof for log stuff; ladders etc.
I would also look at a wooden building for warmth etc especially if you plan to work in it (not that you can't get a concrete one warm, its just easier with wood.
For bike security if you go with wood look at shedshackles that essentially require the whole thing to be demolished to get a bike out I've got 2 of these and they would take hours to shift even with power tools
