cost of building bedroom over double garage - anyone know?

[nikos]

We've seen a house we really like but to make it big enough for us all we would need to build a bedroom over the integral double garage. Anyone give me a rough idea of costs? Would imagine the foundations are strong enough already without underpinning as it is a relatively new house.
Thanks

[GrendelsMum]

This has some rough estimates for various common jobs:

cambridgebuilders.co.uk/rates.htm

[nikos]

Thanks for that, but it doesn't give cost ofbuilding on a garage. Wonder if anyone has had it done?