Since this is a home builder website like you said, you first need to ask the question: what keyword group are you targeting?
Are you targeting a generalized city, keyword or (as you mentioned) are you targeting home/retail consumers looking for model numbers. If the later, you should alt tag using the appropriate model number, and possibly even a short description along with it if it allows.
Don't try to rank each page for all of your keywords either, pick a few kwds per page and you will be on the right track.
I have been lurking around several SEO/SEM forums for some time now. I understand the importance of page titles, unique page descriptions, ALT tags, etc. However, I have taken over the design of a once very non-SEO page. Over the past several months when time allowed me, I now have everything else except I am stuck on the ALT Tags.
The company lists their options (home builder) so anything from kitchen cabinets to hardware, to flooring are listed. I don't want to be repetitive on the ALT Tags by saying: "xxxx option offered at Xxxxx Homes"...I then thought about listing the model number for appliances, flooring choices, etc. Would this be my best bet?