Builders FirstSource, Inc., Dallas, TX, a supplier and manufacturer of structural and related building products for residential new construction, reported sales of $411.1 million in the first quarter ended March 31, 2007, down 30.2% from the same period a year ago. Profit was $0.2 million.   ;   ;   ; We continued to face very challenging market conditions during the first quarter,' said Floyd Sherman, Builders FirstSource CEO ."The combined impact of decreased housing starts and lower market prices for lumber products reduced our sales."   ; Builders FirstSource reported a decline of 36.2% in housing activity in its markets. Also, commodity lumber and lumber sheet goods prices had a 5.7% negative effect on sales.   ; The company said it expects difficult market conditions to negatively affect its operating results through the end of 2007 and possibly into 2008.