Greenhouse?

Since you don't have snow I'd make it from pressure treated 4x4 corner uprights with two 2x6 x 12' side beams supporting 2x4 x 10' purlins. Southern yellow pine (SYP) is nearly as strong as oak. I use beams one size larger and 2x4 x 4' diagonal corner braces to hold a heavy snow load.

Suntuf polycarb holds up well as roofing.

You're describing a conservatory. Nice enough if you can afford it, I guess. If steel and powdercoating is cheap enough and you can get sufficent glass free, perhaps it would be, though you'll need a lot more steel to hold up glass than for twinwall polycarbonate rigid glazing, or rolled plastic greenhouse cover. On the plus side, you're describing small, so it won't be that hard to make it strong enough.

Remember that greenhouses need adequate ventilation, or things cook in warm (or even cold but sunny) weather. I don't know if you have anything useful in the way of agricultural extension with all the CA budget crises, but if you do, find your local extension agent and see what they have for info.

Or look here...(but it's from an eastern state with real winters)

--Winston

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Good for you.

Google on hydroponics (25,300k hits) or aeropoincs (783k hits) and review what other people have done to avoid reinventing the wheel. Aeroponics seems to be the current hot trick.

To avoid raising supermarket produce [not generally cost effective] you may find the following urls helpful.

I Googled but got discouraged when my first few hits were folks selling stuff rather than general info, as you've provided here.

Thanks, Unka' George!

--Winston

My view, hydroponics just adds unnecessary expense...

I built Milady a high tunnel greenhouse. Crops grow in the soil. Roll up sides and end windows for ventilation. because of my MN location, I did put in a small propane heater, you wouldn't need it.

Karl

Thanks, Jim.

The lumber I can get isn't nearly as stout as that available elsewhere, based on the casual 'swayback' look adopted by the 4x4 floor joists in my tiny storage shed (over only 8 feet).

I will add four concrete piers at the midpoints (5' and 6') and at center to make the floor look kind of flat.

To CAD I go!

--Winston

Thanks, Karl. The professional and efficient grounds crews employed by one of my neighbors like to rid themselves of concrete scrap by launching it over our common fence, so I require hard walls to survive the bombardment.

--Winston