well.. what ill do is build a table.. 8x4 feet with 6 inch high walls.. line it with a tarp, drill 8 holes, each hole in the center of a 4 square foot area, and using some waterproof silicone glue (unless thats unsafe for plants) i would glue in some PVC drains.. or maybe just capped 1/2 inch PVC pipe with drain holes drilled in it.. fill it 4 inches high with white pea gravel (itll weigh about 600lbs).. and connect the two rows of four PVC drains together, and bring them together in a T... then run all that into a tote which will contain the nutrients and a pump to flood the gravel... so an 8x4 foot table with pea gravel using an ebb and flow system... all that with a 600w light in an oblong reflector so i can cover to the edges of the entire table on the back and sides of this table i want to staple or glue some white poster board to keep as much light inside as i can... and i will hang ropes along the back edges where the vine plants can grow over... and everything will be on a timer too also.. since this will be in my basement, and im not so sure how much this light will effect the circuits here, i might as well get a breaker and some wire to wire in a dedicated circuit to the hydroponics... in total.. $100 for the ballast, about $20 per bulb, which i only need one at first cost for totes, PVC, and wood should go to more than $50-$60 the gravel shouldnt be more than $20-$25 breaker, wire, and a pump maybe another $20 so in total this should cost much more than $250... and under $40 a month in electricity, nutrients, and replacement bulb costs

What is the cover material made of? Is it shade cloth? That's fine, but it comes in different kinds that allow in different levels of light. You will have to find the one that suits your weather, and you may have to change it at different times of the year. If you attach it with wiggle wire, you can take the cover off and on easily. The cheapest way to build your tank is to simply make a wooden frame and put a pond liner in it. I'd use 2x12 or 2x10 treated lumber. Put 2 metal brackets on each corner to reinforce it. Obviously, keep any sharp edges off the pond liner. My own design for a lid uses a very common white fiberglass paneling that comes in 4x8 sheets. Sandwich a layer of styrofoam between two pieces of that paneling, hold it together with galvanized bolts and washers, and seal the edges with clear silicon. The lid is the most expensive part, but it lasts forever, and your tank will cost very little compared to buying a pre-formed plastic tank. You can get by with just styrofoam as a lid, but it will wear out much more quickly.

Given that we're discussing hydroponics it's funny that you'd worry about the weight. A soil farm would be the real concern to a structure. Picture this: Primary nutrient tanks stored at ground level with solar-powered pumps used to top off smaller (but still sizable) reservoirs strategically positioned over the best load-bearing structures of the building. This could then be pumped out to the plants that need it in standard hydroponic grow bags and such (light-weight stuff). The reasoning here is that ground-level tanks don't weigh down the building, are more easily accessible to larger equipment, and if buried would even help keep the temperatures more ideal. Reservoirs on the roof allow for smaller pumps to handle the distribution to plants (since those pumps wouldn't be required to support a 15-20 foot head). Additionally, the buildings could be topped with plastic sheeting like an inflatable greenhouse. Given the amount of weight that the building has to be able to support simply in terms of roofing personnel and equipment for routine maintenance, I don't really think there's a lot to worry about. Older buildings would probably need an inspection at the very least to make sure it's safe, but your average strip mall or supermarket would be in good enough shape to handle a couple tons of evenly-spaced goods on the roof. Plus, they wouldn't have to worry about wind and rain damage to the building's roof anymore.

There's a lot of things you can use as your hydroponic medium. Sand, gravel, even sawdust (certain kinds) can be used under various conditions. Be careful with what kind of non-hydroponic pH up and down you use. The aquarium stuff isn't bad, but it can potentially cause precipitates in your solution since it's not really designed for use with hydroponic nutrients. I'd also recommend some moderation in your initial gardening attempts. There's not a lot of expense (beyond personal labor) in large backyard soil gardens, but going large-scale like that in hydroponics will nickel and dime you for months. When you're comfortable with your current hydroponic system(s), employ the doubling rule. Double whatever you've got until you've got as much as you want. But always wait until you've got mature plants in the new systems before you decide you want to double again. Everything else, let it grow in the dirt where it's much cheaper. I may grow some hydroponic potatoes or carrots some day, just to see what it's like, but if I want to have a garden of those for eating I'll most likely just plant them in soil. So that's my advice: Build a "normal" garden and let your hydroponics take it over gradually.