I don't know exactly what you mean, but "vill har" never works. It's "jag har" or "jag vill ha". Note also that "svart" doesn't change, I mean that you don't add a "t" with the t-nouns.
So you can say "Jag vill ha svart kaffe" (kaffe generally is a t-word) or "Jag vill ha en svart kaffe" (if you refer to a cup of black coffee).
Jag vill ha starkt kaffe.
Jag vill ha en stark kaffe.