The flexible sheets are attached to {HEAD ~ structural members}, that is, to purlins beneath {TAIL ~ the roof panels} 
The flexible sheets are attached to { HEAD ~ structural members } , that is , to purlins beneath { TAIL ~ the roof panels }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL