Should I Scarf or But

I am planning to build a 5Wx10Lx4H tear or one similar to the Baja Benroy. If I can not get 5x10 ply how should I join the 4x8's together? would a simple butt joint work or do I need to scarf them? Mike if the Baja Ben is 6' wide how did you do the roof? Thanks for all the help, everyone. Sorry for asking so many questions
P.S. Mike don't you have a step by step build of the Baja Benroy? I can not seem to find it for the life of me.

P.S. Mike don't you have a step by step build of the Baja Benroy? I can not seem to find it for the life of me.
