I built the frame from quarter inch plywood i got at home depot. The grow bed I bought a food grade plastic food service tray. The "Growbed" is basically an oversized overhead sump which i filled with hydroton clay pellets. I have photos in my post that show the setup.
I also grow herbs and veggies aquaponically and hydroponically....so from my experience the easiest herbs to propagate into a system is definitely basil and mint. They are both just cut and plant, once the basil cutting is in the water, it will root in a couple of days. It also grows quite quickly.
Are you providing light to the plants?