I did a white spray and used one can of white and one can of clear gloss - looking back I could probably have used another can of the clear coat

Depends on your surface preparation. Do it right and you can get away with very little finish. No more than a single can of colour in any case (usually just one or two coats), but clear coats could run to three cans (I've known guys use five).

On the other hand, I know a guy in the States who can do an LP top with a single shot glass of clear...

thanks, my next question,any prefered method of spraying with rattles?

Dont know about anyone else, but I found a spray gun very handy (probably got the wrong name for it, but its a plastic thingy which clips over the top of the spraypaint allowing you to operate it with a trigger). So much easier, less fatigue and gives an even spray.