August has been a rough month for CBS sitcoms, with sources saying network officials have indicated that two in-house shows, “The Building” and “The Boys,” won’t be extended beyond their initial order.Warner Bros. is also fighting for its life with two series occupying the 8 p.m. hour Wednesday –”The Trouble With Larry,” an early-arriving fall comedy — and “Tall Hopes,” which both premiered Aug. 25. The network hasn’t formally made a decision on either show (they’ve aired twice), but at this point just one CBS summer comedy, Paramount’s “Big Wave Dave’s,” looks likely for an extension. That show, however, got sacked earlier this week by the big Dallas-Washington “Monday Night Football” showdown, falling to a 13 share after retaining 93% of its “Murphy Brown” lead-in rating in four previous airings. CBS stated in July that it would use the summer as a testing ground for midseason series, which could then be re-ordered and return later in the year. Thenetwork also said short orders provide more at-bats with new series, while suppliers expressed fear that the practice will prompt quicker hooks in evaluating low-rated or marginal new shows. As a side note, Bonnie Hunt, star and exec producer of “The Building,” has a movie deal that would make it difficult to immediately continue her series, produced by David Letterman’s Worldwide Pants Inc. in association with CBS Entertainment Prods. and Columbia. Neither that show nor lead-out “The Boys” (from CBS and Twentieth TV) helped their cause Friday, posting an 11 share each in the 9 p.m. hour.