DIY. People here may critique your plans, but most won't draw out the plans for you. So try drawing something up first. Maybe use Google Sketchup. It's free and a valuable tool, which is worth learning if DIY projects are your thing.
Just do a basic tried and true design like this, but extend it to lenght you need to be. 2X4s for the entire construction will be fine for your project. As long as you can cut wood well and can screw things together true, you'll be fine http://www.youtube.com/watch?v=uTmxG4N_V10