It is a long time since I have bought tiles so I have no idea if your tile choice is cheap or expensive. Perhaps, if a particular tile of a particular cost per m2 is chosen for all the balconies, unit owners could be given the option to substitute a different choice if they pay the difference in price. To avoid it becoming a big job for the manager or EC, those wanting a different choice could be asked to source and provide the tiles and be reimbursed the lesser cost of the standard choice. Alternatively, unit owners could be restricted to making a choice from a particular shop which then collates the bulk order and tabulates the extra charge to be billed to unit owners for non-standard choices.
It is probably a big enough job for someone on the EC as it is so I could sympathise if they are resisting what could turn into an exercise in herding cats. I suggest making it very easy for them if you would like choice.