[eonw]

knowing what materials you have available would make it easier to help come up with a design.

shipping containers come to mind as something easy to acquire and redesign the interior of quickly and easily.

if wood is in abundance, there are many cheap and fast designs for small shelters/houses available online that have been made for ease of construction. Wood is probably easier/faster to build to earthquake resistant building code, then other materials.

small and efficient home design is often studied in architecture schools, there is an abundance of designs available online. if you found one suitable, ask the creator if they would be willing to provide your cause with a free set of blue prints or more detailed design materials.