It’s probably gonna cost more than $15,000…..even for a pole barn with dirt floors
Materials will probably be around $10k for cheap stuff. Windows, doors, and electrical all add up too.
I hired out a 24×40 stick built with 16′ sidewalls, 20×14 insulated door, vinyl siding, asphalt roof, floor drain and concrete floor. It was about $40,000 with some dirt and tree work. It would have been a few grand more but I did the electrical work.