As a rule of thumb, +50% is not too much, and +60% is safer. It's quite surprising how much cloth the camber and pockets use up. To be absolutely safe, it's best to draw a cloth layout, especially if you're making each main panel out of one cloth. There's usually some spare cloth on either side of the panel shape, which may or may not be usable for pockets, depending on panel width. Remember to lay the panel pattern out on the cloth such that the threadline is as near to parallel to the leech as it will go, and doing that, in a kind of chevron or zigzag pattern, makes it more likely that the offcuts are useful.