Confusion when describing the location of something using A在B的location pattern?
in terms of grammar, both sentences are ok. but the two sentences emphasize different points.
i'll put these two sentences in dialogues of English so that you can get a better understanding.

For 图书馆在宿舍的前面:
-Where's the library?
-The library is in front of the dorm.
(This is probably what you want in your case, emphasizes the location of the library-WHERE)

For 宿舍的前面是图书馆:
-What's in front of the dorm?
-The library (is in front of the dorm).
(Emphasizes it is the library that lies in front of the dorm-WHAT)

-native speaker here, hope this help :)