For the building, they need to transfer money and gems to the person who is going to build it. I will look into the options currently available on this. For upkeep, they simply need to drop it into the coffer.
Couldn't the system be modified as follows:

Dwelling owner can during financing authorize certain individuals to "interact" with the construction project. As in, authorized players can contribute their own gems, gold, and turns directly. Otherwise, it becomes very difficult to transfer gold, and any gem transfer would likely be one per day, correct?