DIY Doctor UK DIY Forums

Hello,
I'm having a 4.8m x 6m garden room built and I wondered what a ball park figure for the insulated concrete base should be and best construction method?
I spoke to local building control and they've confirmed its within permitted development and they also offered advice.
The building control surveyor suggested a layer of concrete, then dpc membrane, then insulation then scree. Also a couple of layers of brick around the edge and tuck the dpc over the brick.
He didn't mention a layer of hardcore underneath, is this required?
There is a slight slope so will need leveling a bit and part of the site is covered in old concrete and I've no idea how deep that is but I'm guessing it needs to come up.
We are within M25 so prices are a little higher than average for UK.
There is space to get a flat bed van around the back, but not sure about a concrete mixer truck.
I know its difficult to price a job without seeing it but any advice on best practice and approximate budgets would be very much appreciated.

thanks in advance
bp

you could install a insulated suspended wooden floor which would be a lot cheaper and a lot less hassle ,