If you have a wide variance in costs for each pizza on the menu, you'll have to estimate your product mix for a pro forma. You can vary the mix and show margins for those mixes. For example, Group A pizzas (high cost) @ 33% sales, Group B (mid cost) @ 33% sales and Group C (low cost) @ 33% sales.
You can also budget costs for toppings and use a simple margin for your estimate. For example, budget costs for dough, cheese, meat/seafood, vegetables, spices, packaging/paper, etc., and use that for your pro forma.
Depending on your market and business plan (delco, eat in, etc), margins run from 20-35%. I run about 24%, but your situation will not be the same as mine.
Since this is your first pizza rodeo, your business will likely not be anything like you thought it would be after a year in business, anyway. You'll change and adjust many things along the way.