Welcome to 2426 Sierra Drive, Upland, CA 91784, an exceptional opportunity to own a custom estate in the prestigious San Antonio Heights. Situated on a sprawling 19,826 sq. ft. lot, this custom home offers approximately 3,855 sq. ft. of main living space, plus a 340 sq. ft. detached guest house above the two-car garage, for a total of approximately 4,195 sq. ft. Built in 2005, this one-of-a-kind residence has never been lived in and presents a rare chance to complete a truly remarkable home to your own taste. The interior is approximately 90% complete and showcases quality craftsmanship throughout, including Saltillo tile flooring, smooth drywall finishes, solid birch interior doors, hardwood flooring, and beautifully appointed custom Spanish tile bathrooms. The thoughtfully designed floor plan features a spacious mudroom/craft room, generous living areas, and a luxurious primary suite with breathtaking city light views, a spa-inspired bathroom with a walk-in shower, soaking tub, and large walk-in closet. The home has received its Certificate of Occupancy but requires the finishing touches to bring this estate to its full potential. The property is currently operating on temporary power and will need permanent electrical service energized by Southern California Edison, as well as installation of a natural gas meter. Additional improvements include exterior paint and landscaping, allowing the next owner to personalize the final details. With its exceptional location, custom construction, detached guest house, and incredible potential, 2426 Sierra Drive offers a rare opportunity to create one of the premier estates in San Antonio Heights. Complete the vision and transform this extraordinary property into the dream home you've always imagined for you and your family.