Most of us use Altex No5 Murray.
You need one 4lt tin to put two coats on a Top Hat. Most manufacturers recommend three coats if applied with a roller.
Two coats last about 18 months max. I personally put on two tins [4 coats] and that lasts about three and a half years.
I save 2 slippings a one tin of paint when I put on the 4 coats. Just done Seaka, last in 2014 and don't expect to slip again till around 2022