My wife and I are thinking of building a PVC pipe greenhouse similar to the one here:
http://www.albertahomegardening.com/an-inexpensive-hail-proof-pvc-pipe-greenhouse/

We're in zone 8b and it gets a little cold in the winters, dipping into the mid-twenties with this last winter getting into the high teens for a night or two (but that's unusual). I'd like to keep citrus/avocados in the greenhouse to help mature them before planting out in our field and also use it for seed starting in late winter.

I've heard an uninsulated, unheated greenhouse can be expected to be about 10 degrees warmer than the environment, so in my mind this would be just about perfect and just about eliminate any freezes that might harm young citrus. The item I'd be concerned about is what to do when things start warming up. We're on a pretty tight budget so pretty much any kind of automatic vents and fans are out of the question. Would it suffice to simply take off the doors on both ends during the summer? It's in the 90s here typically in the summer and so I'd be concerned about frying our plants (especially the citrus). I'd love to leave the plants in the greenhouse year round to save on hassle (plus I don't know where I'd put them if I got more than a handful of citrus trees). The only other concern in taking the doors off is wind. We almost always have a breeze going and often have 20+mph gusty winds. If feels good on a hot day but I'm wondering if taking the doors off my greenhouse will cause problems with wind whipping the structure too severely. Any advice from those in a similar climate is very welcome!

I'd suggest building one out of treated lumber and covered with 4 year plastic. You must have sides that open 100% to avoid frying the plants in the summertime. You really need a greenhouse in SE Texas for only a few days a year!

MrTexas, do you know any place local to the Houston area to buy 4 year plastic and other greenhouse supplies? I've been looking at places online but it seems I could do better if I consider the shipping. Thanks for the help!

http://www.growersupply.com/4yearpolcutb.html

A friend had his 4 year plastic last a couple years longer.

Build your greenhouse at least 2x as big as you think you need.

try this for a picture of the type of GH I'm talking about:
http://pjsauber.fortunecity.com/Greenhouse.htm

I made my greenhouse based on alberta's web page with some adjustments , including 0.15 poly thickness/uv resistant/condensation protection

Here are some pictures






But there are something more to do:

1 I have only one entrance ....> should I make two of them or it will be too "windy" inside ?
2 I need to place some shade cloth up on the greenhouse ....>testing 2 days inside got me few fried plants, what is the recommended shade value for citruses (30-40-60%)?
3 How could I add some side windows on a poly ?How to secure them without damaging the poly

Nice work!

Thanks!