If you are going to veg for a month or so before you flower you will need atleast a 3 gallon pot, a good rule of thumb is 1 gallon for every foot of growth, your plants will be about a foot tall after a month, when you flower expect them to stretch 2-3 times their size. So for a foot tall plant switched to flower will end up being 2 or 3 feet tall, so a 3 gallon pot would be ideal, if you want bigger plants you will need even bigger pots.