In most buildings you need to have separate restrooms (facilities) for male and female users. So technically, doing a pair of unisex restrooms isn’t allowed.
However, in the 2012 IBC there is an exception 2902.2.1 for family or assisted-use toilet facilities. This is great for institutional users or rec facilities and other uses where you may have a lot of single toilet restrooms. Its especially useful if you want to put a shower in one but not the other. It states:
Where a building or tenant space requires a separate toilet facility for each sex and each toilet facility is required to have only one water closet, two family/assisted-use toilet facilities shall be permitted to serve as the required separate facilities. Family or assisted-use toilet facilities shall not be required to be identified for exclusive use by either sex as required by Section 2902.4.