Getting a modular structure that comes as a kit is the cheapest option for a backyard guest house—some products cost just under $6,000—but that price tag rarely reflects the final cost.

Kit homes are an increasing popular option for home buyers looking for a cost-effective way to build their own house or ...

So, Eva, 31, researched building a cottage in her own backyard ... a detached unit or installing a prefab one. Over time, you could rent the ADU for income; house a parent, child or caregiver ...