I calculate how much money I get in return for every dollar I invest in a type of seat. If I invest $200 in a seat that sells for $12, I get 12/200 = $0.06 dollar in sales for every dollar I invested in it (so you divide your ticket price by the cost of 1 seat). Of course, you need to sell the seat for this to be true, so this calculation is only useful for seats you are selling out. If you are regularly expanding your arena, you should lower the price of the seat you're not selling out (unless that seat's return is already low, then you won't expand it even if it sells out).
Keep in mind this is only 1 way to build your arena, there's other ways. Mine is to get the quickest profit, so you'll have more money sooner to keep investing in the arena. There's other factors you need to take into account; the total attendance cap (~22.000, you should think about it when you reach 12k bleachers), the price stability of the more expensive seats (if return is about equal, build the more expensive seat) and wether you are close to promoting or not. If you promote, sales will go through the roof at first, and then fall back down. On top of that, you will most probably lose many games since you'll face better competition, and in that case it's much better to build the expensive seats, as those fans will care less about wether you win or not.