Most Las Vegas valley casitas Kingdom & Co. builds fall between 500 and 1,200 square feet. The right size depends on the intended use. A 500 square foot casita with a bedroom, bathroom, and kitchenette works for most aging-parent and adult-child use cases. An 800 square foot casita gives the resident a true one-bedroom apartment with a full kitchen and living area. A 1,200 square foot casita (the maximum allowed for a detached ADU in the City of Henderson) approaches a small home, with room for a bedroom, separate living and dining areas, and a kitchen that supports actual cooking rather than just reheating. Final size is governed by your lot size, your jurisdiction’s code, and your HOA’s architectural review committee.