The balls end up being about an inch to an inch-and-a-half in diameter. As long as the Rolo is covered, and you don't see little bits of it sticking out, you'll be fine. The more dough you use per cookie, the thicker the cookie part will be so you will have to cook them a little longer - you will also get fewer cookies. It's totally a preference.
(This is only one batch, I had another in the oven)
You'll know the cookies are ready when the bottom edges (closest to the cookie sheet) are just slightly brown. A few of the cookies may also start to brown a very little on the top in the center. Don't over-cook them because the caramel in the Rolo will harden quickly once they cool if they are over-done.
Once you have pulled them out of the oven, allow them to cool for 2 minutes on the cookie sheet before transfering to a cooling rack. Also, I would suggest twisting the cookies on the sheet before you try to remove them with a spatula. Sometimes the bottom of the cookie will stick to the sheet causing the melted Rolo to stay on the sheet, leaving you with a hollow cookie. Allow to cool (or not, they are DELICIOUS when eaten warm), and enjoy! Store in an air-tight container (i.e. Tupperware) to keep the carmel center chewy.
One of my favorite, and easiest cookies to make. I promise you'll be addicted once you've tried them. And no, I haven't already eaten 5 of the ones I just made this afternoon...........
Family Update: Justin and I found out we will be having a baby boy in September, and we couldn't be more thrilled! The pregnancy is going very well, and we love looking at (and occasionally purchasing) cute things for our little man that will be joining us in just 4 months time.