You can also call a “sap shack” a “sugar shack” or “sugar house.” Sugar houses remain common on the Vermont landscape. The gable roof, the sheet metal roof, the ventilator, and the (possible) woodshed on the rear of the building are indicative of a sugar house. To read about Vermont agricultural buildings and their significance, read the Multiple Property Document Form – Agricultural Resources of Vermont. Sugar houses are on page F-102 (or 151 according to adobe PDF).
Regarding this particular sugar house, all that turned up in a search was a 2008 photo of the building – abandoned then, too.