How To ADU - My #1 learning resource for ADUs. There is so much great content on here from budgeting, to breaking down legislation, Justin is a true expert, and he’s a funny, likable guy.
From his channel: ”If you own a home and are thinking about building an in law suite, granny flat, guest house, or an ADU (a secondary home on your property), then I'm going to help you step by step….”

Robuilt - Rob is a Airbnb investor who started his journey by house hacking and building an ADU in his back yard in LA. I was originally turned off by his clickbait titles and thumbnails, but his content turns out to be incredible for aspiring AirBnB real estate investors. He’s also an entertaining, down-to-earth guy, who just happens to have a wealth of knowledge he wants to share with the world.

KerryTarnow - Kerry’s channel is focused on prefab homes, but there’s significant overlap with ADUs. He’s entertaining and a great source of what’s happening in the prefab world. Highly recommended if you’re considering prefab.

Epic Monday - Investor focused resources with a catalog of prefab houses and a calculator to help you calculate rental income.

Housable - This is the website I used to A) evaluate my property for an ADU, B) get concepts drafted, and C) get full blown architected and engineered plans (with many rounds of corrections) to submit to the City.

ADU Solutions - Tons of great information on ADUs , including types of ADUs, ADU regulations, and information on how to get started. They even have a step by step guide that will walk you through the building process, including assessing eligibility.