Remember, my greenhouse is attached to another building so your roof may be different than mine. Because my is only 4' X 8' and the roof ridge is the 4' length I didn't use cross supports. I made the roof ridge extra long and made a scroll cut to add some detail to the project.
I supported the ridge beam with a 2" X 4" from the top of the front frame.
I notched the rafters to fit over the top of the frames.
Basically I built the roof in place cutting to fit. If you have questions or want more detail just drop me a line and I'll help you out.
Next time we'll add the glass panels.