PLEASANTON — PG&E will be able to expand its East Bay presence after an all-cash purchase of a Pleasanton office building and an adjacent parking garage from Workday. Oakland-based PG&E paid $21.8 million for the building at 5918 Stoneridge Mall Rd., according to documents filed on Jan. 29 with the Alameda County Recorder’s Office. The assessed value of the building and garage is a combined $72.3 million, including the $67.3 million assessed value of the office building specifically, public records show. This means PG&E bought the office building and garage for 69.7% less than the assessed value of the property. The building is large enough to potentially accommodate 800 to 1,000 PG&E workers, based on typical guidelines for office sites.