TBM, I a few years back I broke up the equivalent of a concrete garage base with a sledge hammer though it was overly reinforced with steel which made it easier the break..! I suspect many home laid garage bases are unlikely to be really solid if you are not up to swinging a sledge hammer then it is possible to hire a Kango hammer and do the job yourself then hire a skip to clear the site if you can not make use of the rubble elsewhere..? madmax has the right idea for an instant garage..(-: Mine was far from ..err..instant.
I suspect having the floor level might be worth thinking about more so if there is any paving outside it in time as having any spills or leaks finding their way out on to the expensive exterior surfaces may be less than ideal..?
I cut a rebate into the edge of the floor into which the base of both the roller door and up &over doors fit, this provides two functions in terms of water being blown in as it runs down the door and can act as support for the bottom of the door in a full on gale, had a few of them here, one trying it`s best at the moment.
Other than that I have a plastic sectional drainage grate system running the length of the doors should either really heavy run off from the hills or spills in the garage overcome first line defences... If you are connecting any drainage to that of the rainwater system of the house, might be worthwhile taking out a water supply and electrics while you are at it..perhaps extend the drainage into the garage to enable a sink to be installed at some later date (-: When I built mine, I just laid in a bit of Kingspan insulation circa 400mm square to allow the concrete to be poured knowing I could easily cut out the insulation at some later stage, to facilitate the installation the water supply and drainage. Also might be worth considering a heat detector/alarm..?
I have a heat detector in the garage space and a smoke detector in the attic space (attic trusses) in my old single brick garage the condensation was horrendous even without the addition of the cycle of introducing heat then allowing it to cool rapidly.... I just wore thermals, even thermal overalls on occasion, to avoid heating, though anything metal in my climatic zone would sweat profusely on occasion, and any bare metal would collect surface rust in jig time, tools included if plain steel..This time round I went for a cavity built construction..Though have little to no intention of spending as much time and effort in it as I did in my old garage..!
Rambled on a bit as ever..(-:
