I decided that 12-15 inches should be my limit. Even though I can afford and would love to have a large aviary, it's not possible cause unfortunately I'm limited with space and the biggest I can have is:
55" width x 40" depth x 35" height
Would that be enough for 12-15 finches?
I know they require more width than height but if it's wider than 55" there'll be no spot for it.

edit: I meant height is 35", with the stand it's 75".