We claim the ornamental design for a roll hoop for a quadrotor model helicopter, as shown and described.
FIG. 1 is a, top, left, front perspective view of a roll hoop for a quadrotor model helicopter;
FIG. 2 is a bottom, right, rear perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a front elevation view thereof;
FIG. 7 is a right side elevation view thereof; and,
FIG. 8 is a left side elevation view thereof.
Structural elements depicted by broken lines have been shown for the purpose of illustrating portions of the roll hoop for a quadrotor model helicopter that form no part of the claimed design.