Abarim Publications' online Biblical Greek Dictionary
The verb δεμω (demo) means to build. This verb is not used in the New Testament but a derived noun is: δωμα (doma), meaning building (hence English words like "domestic"). Our noun occurs 7 times; see full concordance, mostly serving as proverbial elevation from which to broadcast something.
The much more common word for house is οικος (oikos), which together with our verb δεμω (demo) forms a cluster of words that have to do with to house-built (follow the link to οικος, oikos for the details).