where to start when you wanna build another home on your property?

Answer 1

With the local building/planning commission. They will know all the ins and out of the process of getting a permit. Without a permit, you risk a visit from local law enforcement part way thru construction, fines, and the possibility of having to tear down/remove what you have done prior to getting a permit.

Answer 2

Planning Department, Health Department, Permitting Department.

Answer 3

Architect