Dave
I do the same sort of thing, and i hate every second of it
I do a walkround of the property with a pen and pad and estimate how long i think it will take me to do each room, i write down any areas that may have a bit more work, ie if i'm in the kitchen and i have the cooker and fridge to do.
Incidently if you do have a cooker then quote that sepperatly, the average price is about £50. Work out how much you want to be paid an hour, i would say between £12 & £15ph, i command £20ph but then i have a good reputation and can get it
Its still rubbish money compared to Carpet cleaning, but it gets your name about
Anyway, if you havent done this before, you will have to add another hour on the job because you will find that it will take you longer than you expected.
Best of luck, and i hope you enjoy it more than i do
Ian