I'm currently building a 14x66 addition on the front of a mobile home. The roof is a 6/12 pitch gable roof covering addition and mobile home. The addition has ceiling joist but I cannot add ceiling joist above mobile home due to gable roof of mobile home. Basically new roof is framed like a attic space over addition and cathedral over mobile home. My question is ... I have a support wall under ridge beam and collar ties in upper 3rd of roof. Do I need struts and purlins to support roof or is supports under ridge beam good enough?