That depends on what you’ve envisioned. Both are great ways to add extra space to your home. For example, adding another story to your house would make a lot of sense if you want to have a modern style loft or have a decorated spacious attic. On the other hand, you might not want to have to go up and down the stairs all the time, in which case, adding a second unit, another room, or simply converting an existing space such as the garage into a livable area makes a lot more sense.
There are several things you need to keep in mind when building an addition. For one, you need to make sure that your project has been approved by the local municipality and that you are not breaking any zoning bylaws. For example, if you want to build a second story, you need to make sure that there are no height restrictions. If you want an additional structure, you’ll need to make sure that there are no land restrictions. The only way to know for sure what kind of expansion is best for you is to consult a design expert who knows the laws and has the experience to see your project through from beginning to end.