This website gives great, step-by-step instructions, and even has pictures of the process. http://www.polkaudio.com/caraudio/subbox/sub_construction.php
Here are your plans (see enclosure). The screens on the porch create a pleasant enclosure.
There are some contracting companies that would be willing to draw up some deck plans for you for a price. You could also get a book on building decks, or buy plans.
You need to consider such things as how to weatherproof it and how to connect the power and other considerations. Your local building center can probably help you with both materials and plans, or if you want to completely "do it yourself" there are websites such as http://www.mavromatic.com/2005/04/diy-wireless-weatherproof-outdoor-camera-rig/ which can help you.
You should look here: http://www.deckplans.com, as it is the best place to go get building plans. There are people here you can talk with and exchange building plans
Plans Now has different plans for building garage work benches. These plans can be found at: http://www.plansnow.com/workbenchplans.html.
The best place to look for such plans would be online at www.mscsinfonia.com. A computer program could be used to replicate these cruise ship type deck plans that could be used for your backyard deck.
An architect or building designer.
Architects.
There are many great free deck building plans online. You can go to www.deckplans.com or www.decks.com to get these free plans.
Here is site with a number of free pole building plans. Not sure if the exact dimensions you are looking for are there, but I'm sure some of these could be modified to work.http://www.ag.ndsu.nodak.edu/abeng/plansGood luck.
Architects.
There are many sites online that provide plans for home building. such as designbasics, saybuild, and houseplans.com. All the sites have different and unique plans that should be looked at.