Splitter A/C in Co-op Buildings

A few top floor residents of our Co-op would like to install A/C splitter units in their apartments with the condenser unit installed on the roof. There are several other residents on lower floors that also might be interested in installing similar units and running it up a stack and mounting it to the roof. This will have to be approved by the board. Does anyone live in a co-op where they have set up a common mounting frame for anyone interested in installing a/c splitters? How was the cost shared, what rules / procedures were put in place? Any other guidance/info?