Building a Winter / Summer grow table is easy. It can be covered with thick plastic sheeting in the winter and shade cloth during the summer months.
...... .... All you need is...
.... ......1. Plastic Shelving
........ ..2. 1/2" PVC Pipe
........ ..3. A cutter for the PVC Pipe
....... ...4. Zip Ties
....... ...5. Shade Cloth or Thick 4 or 6 mil Plastic Sheeting
The plastic shelves can be purchased at most hardware stores or even at Wal-Mart. They cost on average $14 depending on size.
Instead of stacking the unit as shown, the shelves can easily be used as tables. You will need solid surface to grow your plants. The purpose is to keep out air circulation that will dry out your potted plants. If your shelves have a mesh or grid surface, cover the table top with a black plastic trash bag.
If you are using more than one table, you will need to zip tie the table legs together before setting up with the PVC pipe. When the legs are not tied together, the PVC pipe will push the tables apart.
Insert the PVC pipe into the leg hole on the table and bend over to the other side. Insert into the other leg hole.
Cover with Nursery Shade Cloth that provides 30%-40% shade. This cannot be purchased at the hardware store. Shade cloth that is available at the hardware store is only 75% shade, which is too dark for growing plants. I purchase my shade cloth online at: http://www.shadeclothstore.com/. They have very good prices and will build your shade cloth exactly to your specifications. I always purchase mine knitted, hemmed, and with grommets. The hem helps the shade cloth keep longer and the grommets make it easy to tie down the material.
In the wintertime, lay down a plant heating mat and hang C-7 or C-9 Christmas tree lights for warmth. Cover the PVC and tables with 4 mil - 6 mil thick plastic sheeting. However, when the plastic is thicker, it allows in less light. Notice how you cannot see through this plastic. Plastic sheeting can be purchased a most hardware stores.
For cold climates, use 2 layers of clear plastic visqueen. This can be purchased online at http://www.discountvisqueen.com/. Large bubble wrap is also recommended for greenhouse insulation. This is a picture of my friend, Brian, in Tahoe. His greenhouse is transparent and is made with visqueen. He also used LED Christmas tree lights instead of the large variety.