The Dane County Sheriff's Office says its deputies and fire departments from the Cambridge and Deerfield fire departments got the call just before 4:30 a.m. Sunday.
The 20-foot-by 30-foot shed was fully engulfed when they arrived.
A statement from the sheriff's office says the fire does not appear suspicious, and the preliminary investigation indicates a possible electrical issue as the cause.
The damage is estimated at $25,000. The shed is a total loss.