ADU or manufactured home?

[Judie Xue]

I currently looking for a place for my mom to live in Sacramento area. She has around $150k cash but doesn't want to take any mortgage. The first option is I can have a contractor to build an ADU for her in one of my rental property's backyard, estimate cost is around $130k for 800sqft. The second option is to purchase an vacant land($80-90k) and put a Mobil home($30-40k) on the land. However I have no experience on ADU or mobile home before. Anyone can give me some advice? Any surprise costs or difficulties I might counter during the process?