Casita and ADU costs in Las Vegas vary widely by size, finish tier, and whether the unit is attached or detached. Stock ADU floor plans start in the $150,000 to $250,000 range for a fully built detached unit under 800 square feet. Fully custom luxury casitas designed by a design-build firm typically start at $350,000 and range up to $750,000 or more depending on square footage, finish level, and site conditions. Detached ADUs cost more than attached due to new foundation, utilities, and standalone framing.