Frame the rough opening to the size of the door. In other words, if you have a 16' x 7' door, make the rough opening that size. Then when you put your finish jambs in, they will cover the edges of the door a bit on the sides and top. On the inside, run a 2 x 4 up both sides, flush with the rough opening. Run one across the top also with the bottom flush with your rough opening. If you are using a door with a torsion spring setup, install a wood block above the center of the opening. A 2 x 8 or 10 works well. Cut is so it fits right on top of the 2 x 4 you already installed and runs to the ceiling. Make sure it is fastened securly. This will provide a mounting spot for your spring pad and opener if you plan on one.
If you are going with vinyl siding, an easy way to do the jambs is to use a 2 x 6 for the jambs. When you install your 2 x 4's on the inside, they will but right up to the 2 x 6's and make a nice solid corner. Once the door is up, cover the jambs with aluminum coil stock and install the vinyl weatherstrips that come with the door. Make sure the aluminum doesn't stick past the 2 x stock on the inside. Any other questions, feel free to ask.