Floor
You need to give careful thought to the floor. Get it right first time. I should have insisted in having a proper flat finish as would for a kitchen floor but what I ended up with is rather agricultural. This causes two problems it is hard to clean up and not very comfortable to lie on. I have got a judo mat to lie which works out much cheaper that refinishing the floor.
Pit
If you want a pit do plan for it now. Much better than smashing up a new floor.
Surface finishing
A properly flat concrete floor can be painted with special paint. Can also get tiles for garage floor.
Damp
Make sure that there is a damp proof membrane under the floor otherwise you will get water coming up from under keeping the garage damp.
Ventilation
Condensation is a problem in lots of garages. Prefab concrete garages can be particularly bad - think about dry lining the walls. Fit air bricks or similar to ensure a through draft.
Roof
It was suggested that I have a metal sheet roof. It looks like the stuff you see on farm building and consists of large sheets of plastic coated steel.
I was told that a felted roof would not last.
I was also told that tiled roofs take much longer to build. Generally time is money. A pitched tiled roof would have rafters which can provide useful storage. My metal roof has much more head room.
Engine hoist
A strong beam or girder can be fitted with a hoist to lift heavy stuff like engines. Plan where you need it early as this may require stronger walls to support.
Walls
Wood, concrete, brick or metal.
