Project Hierarchy or Master Project

When you have a project that is essentially made up of smaller projects. An example might be you have ten homes being built and each home is to be a project but they are all being built for one client who want one bill for all ten homes but you need to track the cost for each home. If the only solution is a set of cost codes for each house it is a management nightmare. It should be simple make a master project and assign the sub projects to the master.