That sounds like a perfect size and a good way to build. My very rough estimate for material would be around $2000 with a concrete perimeter, sounds like a reasonable bid.
What are wooden gutters you refer to?

I was looking at rain chains once and saw a picture of gutters,made of wood,instead of aluminum. If you google image "wood gutters", some nice pictures come up.

The contractor is going to call about getting them made, but might have to possibly make with pieces and silicone like CRAZY!! :)

He thought I was crazy when I first mentioned it, but after seeing pictures, he was intrigued.

If it's going to be too hard to do, or too expensive, I will just do seamless gutters and still add the rain chain that will go into a rain barrel.

Thanks for the imput and feedback!!

The pea gravel floor is a popular option but not practical at all. It gets very unstable and slippery when wet. River rock would be a better option. Consider decomposed granite though. The DG is many different sized particles of granite that pack down and form a solid, stable floor, but remain porous. I wanted a paver deck in my GH and used DG as a base. After laying the brick pavers over the DG that baby is smooth, flat, non-skid, porous and hasn't moved one iota since the day I put it down. Cheryl

My previous house in the Seattle area was built about 60 years ago and had solid wood (i.e., one-piece) gutters milled out of clear, old growth cedar. They were nice-looking and you didn't have to worry when you leaned a ladder against them. However, if you don't keep them cleaned, they can still rot, especially if they are not cedar. Further, this kind of gutter is very hard to find and costs a huge amount compared to other materials.

If you are talking about constructing a gutter out of pieces of wood and siliconing the joints, I would discourage you from doing this. Wood has movement due to moisture and even silicone will fail in a short time under wet conditions like this. If you don't like the look of metal or plastic gutters, you might use them anyway and box them in with wood for the aesthetics.

To me a greenhouse isn't about the materials as much as it is about what environment you want and how will you achieve that. A couple windows and vents isn't much for temperature control. Sounds like you will be stuck with using heavy shade cloth in summer to hold down temperature. Around here a greenhouse of your design could hit 100F or more in winter, 150F in summer unless heavily shaded.

Knowing your crops, climate, and objectives (all year, part year, etc) are necessary to determine optimum design.

While I like the idea of wood gutters, it is something that we decided against.

What would you suggest for keeping the temperature lower?
Two more windows on the backside?

It's not going to have electricty, so that is why fans weren't included.

Thanks everyone for the imput!

Without electricity, using only passive ventilation, you should plan on seeing temps 20-30 degrees above the outside temp. 120+ degrees inside the GH is tough on plants.

The other thing to consider is the day/night temp differential. Minimizing this temp differential is important in order to minimize internodal stretch in your plants.

$5K is a lot to spend without putting in electricity and an exhaust fan.

http://www.igcusa.com/Technical/coolingsystem-type.html
http://forums2.gardenweb.com/forums/load/strucs/msg0218442911978.html

I agree fully with stressbaby. Won't pay that much for a greenhouse that really isn't useable for much. Better to buy a properly designed system from a major supplier. But first you need to define what you want to use the system for and what controls that requires.

If you just want a high tunnel get one with roll up sides. That will hold inside high temperature within about 15F above outside.

Top link that stressbaby posted is below.

Here is a link that might be useful: temperature control systems

The above posts by fruitnut and stressbaby , citing 100 deg. +++ temperatures inside a greenhouse of your design, should be considered as very important factors in your plans.

Field studies of passively ventilated GHs, using a minimum of 20% roof vent area and 10% floor vent area, show that the GH will still be at least 10 deg. warmer than outside.
For your 256 sq. ft., that would be 50 sq. ft. of roof vents and 25 sq. ft. of floor vents.
Heavy shading could help with the temperatures, but the reduced light would significantly lower the yield of fruiting crops.

Here is a link that might be useful: ventilation

The temp control link was a good one. He is coming by tomorrow to do a quick plumbing job for me and I will show him the diagrams and come up with some solutions.

He is also going to add in electricity to the building for no add'l cost.

Thanks everyone!

So I think fro ventilation we now have some better plans.

Since I will have electricity, a couple of fans/exhausts will be nice. I will also have gable vents that he is going to make covers for to put up on the inside and then a few of the panels on the sides will be installed, so that they can be removed if need be.