The ornamental design for a restaurantbuilding, as shown and described.
FIG. 1 is a perspective view of a restaurant building;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a left view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is an alternative perspective view thereof.
The broken line showing sidewalk and parking in FIG. 1 and FIG. 7 and the broken line showing benches and panels in FIG. 1, FIG. 6, and FIG. 7 is included for the purpose of illustrating environmental structure and forms no part of the claimed design.