As I walked into the family-friendly, casual restaurant, this sign was on display:
“Build your own nacho”? As I wondered in a tweet a little later, what if you want more than one nacho? Do you have to go through the line again? Or are these really big nachos? Looking at the sign closer, I see that the restaurant gives you the chips, plural, so we can cautiously assume that you can acquire several nachos in one pass. Also, I see that the sign has been carefully punctuated. When I first saw it, I parsed it like in this diagram. Here, the entire phrase build your own nacho has been pressed into service as a compound adjective. It’s a bar, of the build-your-own-nacho variety, similar to build-your-own-baked-potato bars or build-your-own-sundae bars.
Now, though, when I look at the sign, I see the judicious use of hyphens suggests a structure more like this next diagram. Here, just the partial phrase make your own has been frozen into a compound adjective, which modifies the nominal phrase nacho bar. It’s a nacho bar, of the build-your-own variety.
So what would a nacho bar of the build-your-own variety be? Context would have to say. It could be a nacho bar that you build yourself, like a build-it-yourself kit car. But given the context, it’s a bar where you build something for yourself, and that something is nachos.
Even so, the structurally ambiguous phrase build your own nacho bar highlights a syntactic tug-of-war that usually hides in the background. You have two competing templates. First, there’s the compound adjective X-your-own-Y template, where X is a verb such as build, make, or choose, and Y is a noun such as sundae, salad, or adventure. Second, there’s the nominal phrase Y bar template, where Y is a noun specifying something that you can find at the bar in question (other than the default of liquor): salad, sundaes, sushi, cigars, oxygen, or in this case, nachos. So when you come across a phrase of the form “X your own Y bar,” where does the Y belong? With “X your own”, or with “bar”?
The X-your-own-Y template is phrasal, and doesn’t put any restrictions on whether Y is singular or plural. It just depends on the meaning you want: Build your own house if you’re only building one; make your own nachos because you typically don’t eat just one, unless they’re of poor quality. The Y bar template is either for a phrase or a compound word (depending on who’s doing the analysis), but either way, attributive nouns are usually singular, so you have gumball machines instead of gumballs machines; car manufacturer instead of cars manufacturer; nacho bar instead of nachos bar. So when make your own nachos and nacho bar collide in a single expression, which one prevails?
The corpora I have access to don’t have enough attestations of make your own nacho(s) bar to make a determination (zero, to be precise), but just doing a naive Google search, I get about 60 hits for each variant.
In any case, remember that nacho bars are not show bars!