Many similar ideas exist. I want to show you how to recycle 2l soda bottles and make a herb garden. The main idea here is that you water from the top and the excess water runs into the 'pot' below and so on. If you build one similar in size to mine you should be able to move it around or transport it easily. It also takes up very little space as it stands almost straight up.
Step 1: Hardware:
1)2l soda bottles.
2)Scrap wood, bamboo sticks, PVC or similar for frame.
Step 2: Tools:
1)Knife to cut tops off.
2)Drill press / hand drill to drill holes through the bottle neck and to screw frame together.
4)Hand saw to cut scrap wood to size.
Step 3: Cut soda bottles.
Cut top of bottle off as shown.
Step 4: Drill soda bottles.
Drill bottle neck as shown.
Step 5: Build a frame.
Build a frame to hold your bottles as shown in the two sketches. Note that the opening of the lower bottle must be screwed to the top bottles' neck. I have not used any measurements because you can make your own custom size. I have made a 5 column X 3 row frame. This could be made to any configuration.
Step 6: Screw bottles on frame.
Screw bottles on frame.
Step 7: Stones, potting soil, planting and watering.
Put stones in the bottom of each neck for drainage. Fill with potting soil. Plant seeds or seedlings and water.