NY -- Standard&Poor's CreditWire 4/30/97 -- Standard&Poor's today has assigned its single-'B' rating to American Builders&Contractors Supply Co., Inc.'s (ABC) Rule 144A $100 million senior subordinated notes due 2007. A double-'B'-minus corporate credit rating also has been assigned. Credit quality reflects ABC's leading position in the wholesale distribution of roofing products, relatively stable product demand, and rising earnings, offset by highly competitive and fragmented markets and an aggressive use of debt because of an active acquisition program. The company is the largest wholesale distributor of roofing products and one of the largest distributors of vinyl siding in the U.S., primarily serving small and medium-sized contractors. Ongoing consolidation in the building materials distribution industry is