change a garage into living room

hi, got a job of changing an attatched garage into a living room, the only problem ive got is the sloping floor, 2 inch drop from back to front. the front is also 6 inch lower than the house floor level, 4 inch at the back, the owner wants it done cheap as possible, can i screed it bearing in mind ive only got 4 inch at the back and 2 inch will be insulation?, or do i take the floor up and relay level knowing that its got re-bar in it and its going to be the most expensive, or can i put joists down cutting them to get the floor level then boarding them out, i think the joists option is the cheapest but the rest of the house is concrete floor, will there be an issue with building control etc?, any info will be grateful

50 mm is pushing it for an unbonded screed.
The best option would be the dig it up option, but I see no reason why you shouldn't build a joisted floor

why not just take up half the floor (the thinner half) then you will get the required thickness

The best (and only realistic) option is to fit a suspended timber floor with full fill insulation.

hi, rang building regs geezer up today and asked him whats the options, says he just come off a job the same and they done the timber floor option, as the cilent wants it done cheap and with less mess i think this is the best option, 3 story house with 5 more attatched i think the neighbors will string me up if i get my kango out at 8 in the morning knocking floors up