Mike is right.
I started last year, bought 6.5hp cheap petrol machine. It managed to clean everything but had to use mostly just the lance with a high pressure nozzle.
Cleaning blocks it got the job done but you'll get covered in crap that flies about.
Cleaning patios was much harder work and a lot more time consuming. Nozzle had to be really close to the slabs and had to go over every square inch....Back breaking.
Bought a 13hp honda 2 weeks ago and the difference is incredible. Driveway that would take 4 hours with old machine took 2 hours start to fininsh including rinsing down everywhere.
It's true what everyone says about buying a cheap machine will end in having to upgrade it and buy a machine that you may as well have bought in the first place.
If you can afford it, get a 13hp petrol minimum. You will not regret it....It does everything much quicker, better and easier.