NFT (nutrient film technique) operates on the theroy of a thin sheet of water traveling on a flat surface touching only the bottom roots of a plant. Many commercial growers use this system.
Two good sources for home built systems are vinyl gutter, and vinyl down spouts. The down spouts are probably better because you do not have to construct a top for them, but most are no more than 3 inches wide and restricted to smaller plants. Do not use aluminum gutter or down spouts for hydroponics. It is possible that one might find larger vinyl down spouts that could be used for any size plant.
7/8th inch holes are drilled on the top of the down spout 8 inches apart. This distance will accomidate most plants that can be grown in a down spout. Sleeves made of 1/2 inch thinwall PVC cut 1 1/4 inches long with one end flared out will fit into the holes and give the plant more stability. The down spouts shown are resting on 1 inch PVC with a drop of 1/2 inch/foot to insure nutrient flow. Eash tube is fed with 1/4 inch od plastic tubing. This will give about 1 to 2 quarts/minute nutrient flow which is about right for NFT. On the inlet end a piece of stiff plastic is glued in the bottom half to prevent nutrient from leaking out the inlet end. The outlet end is suspended over a 30 gallon garbage can that catches the free falling nutrient. In the bottom of the can is a 170 GPH submersible aquarium pump. The pump runs 24 hours/day when first planted, and from daylight to dark when the root have begun to grow well. There is a piece of wood tied across the top to prevent the down spout from rolling over as the plants get large.