I don't have a greenhouse yet but have been doing some research because we want to build one this coming year.

First off, we are going to use tubular steel instead of wood. Where we live, termites are a constant maintenance issue so the metal works better for us.

I am trying to make up my mind as to what would work better for me and I have been looking at both the corrugated fiberglass and polycarbonate panels. I like that you can get polycarbonate panels that are somewhat insulated and they also come in a variety of choices. On the other hand, the fiberglass is readily available and may be better as far as being UV resistant. I have heard that most polycarbonate is only UV treated on one side. So, I'm still investigating. I'll be interested to see what people that actually have experience have to say.
Good luck and I hope that you post pictures.

As stated, the wood will be an issue in the near future. We use poly greenhouse covering, you can buy rolls of it in the mil-thickness you want and the life span needed (up to 5 years here in AZ). Polycarbonate panels are the way to go but they are expensive, if you go that route use the twin walls, I use the polycarbonate panels on my house and am very pleased.
What you really need to look into is the systems your going to be using for cooling/heating and to do that ask yourself "What am I going to be growing in there year around?"

I want to grow garden style vegetable. Like tomatoes, spinach, lettuce, radishes, beans, onions...stuff like that. My hope is to be able to grow them year round and provide my family with fresh veggies. I have about 5 raised beds right now, but the summer is killing all my plants so a year round GH made sense.

I was thinking about doing a hoop style GH but was worried about how to attach the panels to the hoops. My brother is a carpenter so using wood was the natural thing to do. We don't have much experience working with metal and thought the hoop house might be to difficult to assemble.

As far as cooling goes I was going to use an evap cooler with vents and vans. My Grandfather has a GH in his back yard with the same setup (welded quonset style with corrugated fiberglass). He passed a few years back so I can't ask him for advice on how he set it up. It's used for storage now (a waste if you ask me) so I have a good idea of how he did it but any suggestions you might have would be appreciated. I'm also looking to see if anyone knows where I can buy the coverings. Is there a place in the valley? Or do I have to order online?

Everything you'll need you can obtain locally, there's dozen's of places that sell all these materials, Since your really looking to grow year around in/on raised beds why not just use a hoop/shade house with 50% shade? I added two 70 foot houses this last season with Alumi-net coverings for hardening off my young grafted fruit trees that come out of the greenhouses.. you'd be surprised how well the Alumi-Net does. Thats allot less cost than cooling and heating a greenhouse

I see you mention aluminet. I have just finished my greenhouse in the high desert (4500 ft 35 miles north of Tucson). My greenhouse walls and roof are 6mm polycarb. You mention a 50% aluminet - does that work for full sun plants? I know the sun is intense here but not being a native and this being my first greenhouse, I'm not sure how much sun to block for cooling before the plants suffer from lack of light. I do have a venting fan on a thermostat. Any advise would be greatly appreciated.