Fire rebuild

Not until the lot is cleared and the debris removal has been signed off, and not until you have a permit. Those two steps run on other people's timelines that are not ours: the debris removal programme and the building department. The honest answer is that the start date is rarely ours to set. What you can do in the meantime is get the survey, the soil report and the drawings under way, because those are on the critical path and nothing about them has to wait for the lot.

You can change it. A rebuild is a new set of drawings, so this is the one opportunity to fix whatever never worked about the old plan. What constrains you is current code and current zoning rather than the old footprint: setbacks, height limits and lot coverage may differ from what was allowed when the original house was built. There are also provisions in California that can help when rebuilding after a disaster, and they are worth checking against your specific parcel early.