Momentum seems to favor KB Home and the broader home-building market as both prepare to post quarterly results this week. Various analysts estimate that KB Home, a Los Angeles-based builder that operates in 10 states, will post a gain of 5% to 15% in sales contracts for its quarter ended Aug. 31 compared with a year earlier, when it reports its results on Wednesday. They foresee a gain for KB Home after larger rival Lennar Corp. last week posted a heady 23% increase in orders for the same quarter.