Many builders are facing higher costs for building materials and having trouble obtaining financing for construction. Some also are facing a shortage of workers in markets where residential construction has picked up sharply, such as Texas and Arizona.An index that measures current sales conditions fell one point to 51. And a gauge of traffic by prospective buyers declined four points to 32 from 36 in January. But builders' outlook for sales in the next six months improved one point to 50. Though new homes represent only a fraction of the housing market, they have an outsize impact on the economy. Each home built creates an average of three jobs for a year and generates about $90,000 in tax revenue, according to NAHB statistics.