Grab a ladder and start adding ribs between the ridge pole and the base. If you plan to take your greenhouse down in the summer (or ever!) do not glue the ribs. Friction fit only at top and bottom. When you are done it should look like this. (that long horizontal bend intentional at this point)
Since attaching the ribs is so easy this step is more about tips and tricks. First, without some kind of fastener the ribs would pop out at the first big wind of the season. To attach at the top and base I chose plastic wire ties. I drilled a small hole through the 45 degree fastener and the rib pole. Be sure there is enough overlap that the hole can go cleanly through both. Once you have the hole slip the wire tie through and secure. See image below.
Repeat top and bottom for all poles.
You should also attach the first and last pairs to the square supports be just wrapping them together with more ties (no drilling needed).
Remember that horizontal droop we saw? Well you should also attach the rib p[airs to the long horizontal bars...Again with wire ties(again no drilling).
Here's a pretty good shot of the completed frame. See the wire tie loose ends on the top right poles? Trim those extra bits off before we wrap in the the next step.