ElkCorp ( ELK), the maker of roofing and building products, said Carlyle Group raised its offer to buy the company to $40.50 a share.Carlyle, a private equity firm, will start a tender offer on or before Jan. 18. ElkCorp's board has approved the revised merger agreement and recommends that shareholders tender their shares. The board continues to advise stockholders to reject the $40-a-share offer from Building Materials Corporation of America. The new offer from Carlyle values ElkCorp at roughly $1.05 billion, including the assumption of around $173 million of net debt. Carlyle was originally going to pay $38 a share.