I claim the ornamental design for a roof mounted hydrant assembly.
FIG. 1 is a front perspective view of a roof mounted hydrant assembly showing my new design;
FIG. 2 is a right side elevation view thereof;
FIG. 3 is a front elevation view thereof
FIG. 4 is a top elevation view thereof; and,
FIG. 5 is a bottom elevation view thereof.
A description of the appearance of the article is as follows: A hydrant assembly with a sleeve and mounting assembly mounted to a roof top. In the figures a hydrant and standpipe are depicted in broken lines and is not part of the claimed design.