when installed the lower end lies under the channel the block plate cannot be removed while the plank brace and the block plate are as shown in fig1 for installing and removing the block plate in selected operative position the plank brace must slide forward in the channel to allow manipulation of leg into and out of a channel aperture 12 g in use the block plate leg slips through an aperture in the channel with the plate 18 a behind the plank brace and with block plate shoulders 18 d engaging the top of in turned channel flanges 12 d it is to be understood that the plank brace may be slid further up the channel to another position without first removing the block plate after the plank brace is moved along the channel to another position the block plate itself is moved into position behind the brace holding it in its new position each of the channel members is supported above a roof surface by spacers s at the upper and lower ends of the channel the entire span of the channels along the roof incline is so spaced to facilitate installation of roofing materials under the channels in order to compensate for deflection of the channel members under full operational weight a movable support 20 shown in fig1 and 6 may be positioned under each channel 12 the movable support comprises a support cylinder 20 a with spaced shoulders 20 b for placement under the channel 12 with the channel spaced between the shoulders the shoulders disengage the channel when the support cylinder is rotated up to 90 u00b0 about the cylinder axis x x u2032 so that the support cylinder can be moved laterally from under the channel the movable support.