Has anyone built a tiny house or cottage in Los Angeles county California?

Me and my husband are 26 and 28 years old. My family has been a property owners for nearly 50 years now, and I have been taking care of the rental property s alone for nearly 8 years now. I am rather poor myself though and make no income from my family s rentals. As I am now pregnant and expecting in may, I wanted to start investing into a real estate property. As many of you may know purchasing a house in Los Angeles County is near impossible if you make under 50k a year. :( So i have decided to buy a plot of land and built what i need. I also am an advocate for green spaces and improving the ability for water conservation so my idea is to build eco smart as well. Does anyone here have any experience with completing this type of custom home? How is the mortgage with this type of project work? Do I get a large loan for a blank lot or should i get a house loan, and hope I have enough to build a house? If I get the lot, what is the title/name of the type of building contractor who will build the house? Are they architects engineers or called something else? Do I have to buy a house plan and per-approve it with the city after or before I buy the land? Land in LA county… Is it possible to find anything under 100k? Lastly building anything custom is expensive I know, but since the house I want is so small do you think its possible to build one for less than 50k?

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