So you want to build you own greenhouse...well there are tons of kits and lots of options.  The main road block I ran into was all the hobby greenhouses were just to small, or should i say to short.  Most hobby greenhouses are around 6 feet tall at the peak.  After all said and done one could fit about 4 Plumerias in a 10' x 10' with a 6' peak greenhouse.  Commercial greenhouses have 12 feet or more in their peaks, but they are huge and cost 7 to 10 thousand dollars.  So I continued my search, until I learned how Rick Stone of Houston, Texas built his greenhouse.  His approach was very simple, take a portable carport frame 10 x 20 w/ 11' peak, and cover it with 6 mil clear plastic, and instant greenhouse.  I have attempted to document the entire process for anyone who wants to build one in the same manner.  Have fun and be careful on that ladder.

Items You Will Need.

1) Universal Canopy, 10 x 20 purchased as "Sam's Club" ($180)
or you can check out their web site...

2)  6 mil clear plastic. Roll size 20' x 100' ($40)

3)  4 to 8 T-Posts ($3 each)

4)  15 to 20 Squeeze Clips (1-$4 each)

5)  18 Ratcheting Tie-downs ($3 each)

6)  1 roll duck tape ($3)

7)  3 rolls Heavy Duty 3M Clear Tape ($5 each)

8)  Options: Heaters, Fans, and Gro-lights

Select a site
Use 2 or 3 people to set up your frame, and as you insert each piece wrap the connection point with 2 or 3 rounds of Duck Tape. This will hold the pipe in place until the tape rots or you cut it off.
Next, attach the Tie downs.  Stagger all 18 evenly over the top of the frame.  This will add structural strength and keep the plastic from sagging and collapsing from rain, snow, and sleet.  Make the straps tight, but don't bare down and over tighten. 
Use at least 4 T-post to anchor the 4 corners of the greenhouse.  Place the T-post on the inside an drive at least 12" in the ground. then wrap at least the top 24" with Duck Tape to secure and eliminate any sharp edges.
Now you must splice two sheets of plastic in order to achieve full coverage. (unless you found bigger plastic) Cut 2 pieces of plastic at 30 feet.  this will give you two, 20' x 30' pieces.  You will splice the 30' sections, giving you one big sheet
of 38' x 30'. why 38' ?  because you need 2' of overlap it to tape or roll & clip the splice area.  I used Heavy Duty Clear tape other people tape and clip it.
("Liquid Nails" works well too)

 Stand on a ladder and pull the plastic
over one end, then move to the other end.
This should allow the plastic to touch the ground on the end caps, but if your overlap was to much and it won't reach the ground on both ends.  However you can make your own end caps or doors with the extra plastic. As shown in the pictures I cut the end cap plastic up about 6' then tape the area so it won't keep tearing, then I pull back the flaps on the ends and clip them back during the day.

Use bags of sand or gravel 
to hold down the plastic on the sides
Use the clips to attach the plastic to the pipe legs. Clip everywhere you think it needs it. Any tears caused by the clips can be fixed with heavy duty clear tape.

This is an inside look, 
notice I cut the excess red strap off.
I hope this helped. If anything maybe the pictures have provided you with some ideas.. There are more pictures in the "greenhouse gallery".