A single-story expansion typically costs roughly PS35,000. This would provide you with a good-sized back or side expansion, as well as the expense of a kitchen, as this is the most popular usage for a single-story extension. It can also provide an ideal setting for a dining room or family room. An extension built on top of your house will generally cost more than one built under it. That's because building codes require that all rooms inside an extension have to be accessible by a fire escape or other means of egress. So, if you were to build an extension only five feet high, the whole thing would have to be enclosed within a fence or some other barrier that prevents any children or pets from being trapped inside. The total cost of your extension will depend on how many walls you want to extend and how large you want them to be. There are several things to consider when estimating how much an extension will cost: size, design, number of stories etc. The easiest way to get an idea of what an extension might cost is to look at some sample plans online. These samples will usually include everything you need to know about price tags and measurements. You can then choose what fits your situation best. Single-story extensions can be built from wood or steel framing.