Function to work out area of items per roll

I have a window tinting business where i use rolls in 36-48-60-72 inch roll sizes. I am having trouble with a function that returns proper roll sizes. The way it works is:

If I have a window that is 23X49 I would pick a 48" roll, because 23 rounds to 24 which is half of 48.

If a window is 60x45 it returns 60.
If 2 windows are lets say 14x28, then a roll size of 48 will be needed.
and so on...

Im having trouble with the equation though, can someone please try to help me. It doesn't work