It will cost about $15k to demolish existing structure with permit and haul away debris.
About 9 to 12 months to plan and build. And about $150 to $200 a square foot to build.
Let me know if I can help.
1). Building designing, reviewing and approval time from city.
2). Your finanical.
3). Finding the contractor.
4). Bay area quality control to approve demo
5). Demo contractor schedule
6). Weather : Don't want to do it at the raining season.
I have built a few homes. Check with me for more details.