I do not the use the garage for a car, it is used for the washing machine, tumble drier and for storage on shelfs.

I would like to make it a little less like a garage while retaining the garage door (thinking of getting an insulated roller door).

The walls are single skin and the floor is concrete with no damp proof membrane (I am fairly sure).

I was thinking of battening the single skin walls with a thick DPM behind, and using 75mm celotex and then lining with ply with plasterboard on top.  This is what I did when converting the rear of the garage last year, which is what the BCO asked for.

The only difference is, in the rear half of the garage I installed a floating floor, with ventiliation below, so any moisture that came through the wall would make it's way below and be vented.

The front half of the garage I would like to keep with the concrete floor, and possibly tile it to make keeping the area clean easier.  How do you go about the DPM covering the outside single skin walls in this case?

How can you prevent any damp rising through the concrete prior to tiling?

Everything is still in the thoughts stage at the moment!

The suspended floor - yes.  Polystyrene sheet would have been fine, but I used celotex again.

This side of the garage is going to remain a garage as such, so was thinking insulating the floor could be ommited.

Sounds like you have the same mixed blessing I have, crap concrete floors. I've (with some help ) dug most of my screed out and replaced it with an insulated floor, a lot of work but well worth it.

I think, as you can get the floor up so easily, you would be well advised to dig it out and fit a  membrane, you could possibly fit polystyrene under the concrete just in case you ever want to change the use in the future, that is if you can fit polystyrene under a  garage floor??

I thought about that, but ?I do not intend to use it as a garage.

I just want something that is easy to clean, and with the door open you get dirt blowing in.

I was speaking to someone who said you can paint that black tar stuff on the floor and ceiling so provide the damp proof membrane, then do what you like to walls (celotex and board).  The floor can also have whatever you want on it.

Not sure if this is the way to go.

If you dig the floor, you can then add UFH as tiled floors on concrete get pretty cold, but depends on whether it is necessary to spend any real length of time in there as to make it worth while.