You can bolster your reputation by using these three words correctly in your next writing.

Buildup (no hyphens, please) is a noun or an adjective: A buildup in troops along the border could be a sign of impending war.

Build up (with a space) is a verb: To build up his reputation in his new community, the young doctor joined the local Kiwanis Club.

Sometimes you’ll see build-up with a hyphen used as a noun or adjective. You’re probably reading some by a Brit, as the hyphen is chiefly British; no hyphen/no space is chiefly American.