It would depend upon your knowledge of CAD programs. For simple one time use then I would also recommend Google Sketch. For more extensive, yet for beginners:
A9CAD
A9CAD - CNET Download.com
LiteCAD
Drawing component 2D CAD CAM GIS ActiveX
LibreCAD
Home of LibreCAD, 2D-CAD
I've used LiteCAD for a bit and it is okay. It isn't for production drawing but good for simple sketches.
When Visio was a separate company, they developed an Autocad clone called Intellicad. Microsoft bought Visio in around 2000 an decided to drop Intellicad. They initially offered it for free to the public then decided to create a consortium to provide future development path. This consortium now develops Intellicad jointly and labels the product under their own corporation (CMS, Proge, etc) for sale. I still have a copy of Intellicad when Visio offered it up for free.
There should be no restrictions on sharing it as it does not have any specific corporate label other than Visio but I'll have to email the consortium (I have a license for CMS version 6.5) to ask about it. But Intellicad is a very good clone of Autocad at $300 vs $4000. Student version is $90.
Concerning your deck; make sure you know your building code restrictions. Some counties have specific size restrictions, ie. if the deck exceeds a certain percentage of the house footprint, it will require permit. Visit your building department and talk to a permit examiner. They will walk you through on just what they expect on the drawings, ie. plot plan & scale, lot description, etc. They will usually have a checklist and a sample drawings for decks since there are many people building them themselves.
I haven't done any drawings for a few years but my last project was a simple deck. One D (24x36) sheet project but they wanted structural calcs which was pretty easy. It took about two drawing days (lazy) but about week total for all the running around. BTW, I did not get paid for that job; the problem with outside jobs.
