Townhouses, duplexes, triplexes, and condos all count as multifamily housing, though the reasons for choosing to build an attached home vary quite a bit. Perhaps you want to live very near extended family, but not necessarily in the same home. Maybe you'd like to generate income by renting out one or more units. Or you simply want to use expensive land in the most efficient way possible, especially in a busy city with limited lot supply.
Families with multiple generations living together have become more common, especially as affordable housing sits out of reach for many young adults. If you have an elderly parent who may need to come live with you in the future, you're going to want extra room. A multifamily house plan gives everyone a lot of privacy while not living far apart.
Duplex home plans consist of two units attached in some way, whether they're stacked levels of a home or side-by-side dwellings. Triplexes do the same thing, but with three units instead. If you want more privacy and sound buffering, consider a design where the units are connected only by a breezeway or a wall that doesn't house bedrooms. On the other hand, if maximizing your lot is a priority, choose a layout with stacked units. In some cases, that may mean that one of the units is on the basement level. Townhouse designs typically feature two more more stories and share one or more walls in common with the adjoining units.
You may be surprised at how impressive some multifamily home plans can be, with upscale amenities like walk-in closets, kitchen islands, private master suites, and porches. Styles vary greatly, too, from rugged Craftsman designs that would fit nicely in the Northwest to elegant country-inspired styles.