Shaz, I think those drawings are great for an initial, "what sort of thing do you want?" sketch. You can work out exact details later. You could do this in SU quite quickly if you want but if you don't get any ideas from the client until you are face to face with them, perhpas the quick pencil sketch is best.
Once you get used to SU, you might do a drawing based upon the sketch they selected to give them a better idea of the look of the piece. This wouldn't include any joinery and might not even have as much detail as I put in that sketch for Bart.
After all the design details are worked out and agreed upon, you can take off with the construction details in SU or in whatever medium you choose.
One benefit to the SU drawing is that many people have a hard time translating a 2D view into 3D in their heads. The other thing that is handy with SU is that you can do quickie drawings of other furniture or walls and windows to give the piece some context and a size reference.
Irony: The opposite of Wrinkly