Re: What is wrong with my roll cast?
If you have a decent overhead cast you should easily have a good roll cast. They are pretty much the same thing. The biggest difference is as you mentioned, getting the rod to load using the water.
In its simplest form, slowly bring the rod up until the tip is past your head and the D-Loop forms behind you. The anchor point should be close to your side. If it's in front of you you not only lose some loading potential but you could hook yourself when the fly leaves the water. Allow the line to stop and plant itself firmly in the water then begin your forward roll cast stroke exactly as you would an overhead forward stroke. Allowing the line to stop plants the line in the water and helps with loading the rod. Many people rush the cast and fail to allow the line to rest and have problems getting a good rod load. Slowly accelerate to a very fast acceleration just before the very firm and deliberate stop. Don't stop low or your fly will stop low and possibly crash into the water and puddle the line.
I just love the grace of good roll casts. There are times in tight streams that the entire day is spent roll casting. They come in handy just picking a fly up in preparation for the next overhead cast, for freeing flies stuck on logs and for getting sinking lines to the surface in preparation for the pick up. A good roll cast is a powerful tool to have.