Hi Brian,
I've had loads of clients paint their roof with excellent effect. As long as the tiles are prep'd and painted correctly, it should last 10 years or so.
Dulux, AcraTex is an excellent product but it can get expensive to apply as you need a Dulux trained applicator to apply it (as OTV mentioned it is a membrane, not just a paint). Colours are fairly limited too.
Dulux also have another product which can be applied by DIYers. Its called Roof and Trim. This comes in 7 (I think) Colourbond colours only (includes Woodland Grey, Surfmist and Jasper so at least there's three decent colours!!).
The reason the colours are limited is that the paint is pre-coloured in the factory using a special 'for-human-consumption' tint to create the colour. Normal paint of course is tinted in a shop, but the tint component isn't safe if water that runs off the roof is to be used for drinking.
Also remember if you're painting the roof, you may need to replace or paint the guttering/fascias too so that will be an additional cost.
Good luck!