They can be designed to set on piers or a concrete slab at the first floor. The walls can be finished with any sort of interior finish or exterior material. A custom designed tower will vary in cost depending on the complexity. Additional wings or rooms will add to the cost. All plans are signed by an architect or engineer.
Plans usually take a month or two to complete.
When done, they will be ready to send to the building department for a permit. All plans are signed by a licensed California Structural Engineer or Architect. Also check your zoning regulations to see if this type of building of this height is allowed on your property. There are often, use, height or property set back limits that need to be addressed. Design is based on having a suitable firm soil material to build the foundation, verify type of soil before building.