This season I built the greenhouse depicted in this plan
In my case, the 1/4" plywood which makes ups the arches was very expensive. In our area all I could find was 1/4" plywood that was clear on one side. After doing some testing on the flexibility of constuction grade 3/8" plywood I opted to use it instead. The only drawback is if there is a large knot at the lower, critical bend in the arch (formed by the plywood), the arch will break at the knot. Of the ten arches I made, only one broke, and that was the first one I bent between the base frame and the ridge board. You have to be careful bending the plywood into the arch shape.

Another problem was the base. The plan calls for 1" thick boards, and over the 12' span of the side, the tension created by the arches will bow the sides of the base inwards. The next time I build a base frame, I will use 2" thick boards and reduce the inward bowing. The last framing problem was the ridge board that the arches attach to at the top. I could not get a 12' board, to make the ridge board a solid, single length of wood. In the end I scabbed an 8' board, to a 4' board to get the 12' run.

The only other thing I learned is that coving the greenhouse frame with plastic in some way infuriates the gods of wind, and no matter how calm it is when you start, by the time you finish you will swear you are enroute to the land of Oz. A good short cut to using batten boards to hold down and reinforce the plastic is to use "batten tape". It is easier to use batten tape than to cut batten boards. I used duct tape for my batten tape, and so far it is working fine. The 3M company also makes a 3" white cloth tape that seems to be holding up well too. My last choice for batten tape would be the Tyvek tape used to hold house wrap to the exterior of buildings. It is weather resistant, has some UV protection, but is fire engine RED in color. You can always paint the batten tape white after you are done to hide its color and to give it more UV/weather protection.. As a last resort you can buy greenhouse batten tape, but that is VERY expensive.

The more you can stay away from "specialty" stores, the lower your overall costs will be, so be creative in selecting materials. So the best advice is to be prepared to be creative, and find solutions to the challenges (construction and wallet wise) that your greenhouse construction will present to you. The minor problems I ran into would not deter me from doing it all over again.