Small units could use electric heat, but it is expensive. A relatively new system uses hot water through pipes in the floor. Heating is usually required November through March, but be sure not to keep it too warm during the day. A good thermostat is a wise investment. Cost of heating is directly related to the size of the greenhouse.
People often ask about using wood burning units, but they become impractical with labor needs.
Once the structure is in place, there are lots of options for benches, lights, mist propagation chambers, bottom heating units, potting areas, sinks and computer control systems. You can use drip irrigation, hoses or misters. The more money you want to spend, the more you can, but you don t have to have all the bells and whistles. Benches can be as simple as a couple of cinder blocks with boards across the top, lath structures or state of the art aluminum frames. You can add to the greenhouse as time goes by, and as you see what your needs are.