The ornamental design for a guide for preparing a building material sample, as shown and described.
FIG. 1 is a perspective view of a guide for preparing a building material sample, showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is another perspective view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a left side view thereof;
FIG. 8 is a top view thereof; and,
FIG. 9 is a bottom view thereof.
The broken lines present in the drawing form no part of the claimed design and are for illustrative purposes only. Additionally, any broken line illustration of environmental structure in the drawing is not part of the claimed design sought to be patented.