March 26 (Reuters) - Germany-based Gebr Knauf KG has offered to buy the building materials supplier USG Corp in a deal valued at about $6 billion.
Knauf has offered $42 per share, a 25.3 percent premium to USG's Friday close.
Berkshire Hathaway Inc, the biggest shareholder in USG, said it may sell its shares if a deal happens.
USG's shares were up 20.6 percent at $40.40 in premarket trading on Monday. (Reporting by Arunima Banerjee in Bengaluru; Editing by Anil D'Silva)