I am planning a 12x8 shed and looking at frame designs on the web. I see a mix of ideas out there that are all presumably just as good as the next. One inconsistency I see is that some roofs have a ridge beam while others have the rafters standing alone.
For a shed this small does it really matter? I plan on using tin on top of OSB for the roof so I imagine it would be sturdy enough anyway.
A ridge board isn't a "beam", per se. It's often just a nice way to bring the rafters together. A proper beam would have a supporting post at each end.
You don't need a ridge beam, but you do need a way to keep the walls from spreading. This can be accomplished with "collar ties", boards spanning the shed at ceiling height, or with large gussets further up the rafter slope. One collar tie would be enough in your case.
I built my 12x10 shed by using 4' by ~18" OSB gussets at the peak of each 2x4 rafter set, essentially resulting in a truss, which proved very solid:
Source: http://halbergengineering.blogspot.com/2010/10/structural-engineering-for-minnesota.html
