Do NOT under any circumstances do this if you are feeling any misgivings. It will turn into a definite chore, and you will probably end up overwhelmed. There is nothing wrong with telling him that you don't want to do it. I understand that he would like to have the quilt made, in memory of his grandma, but most people have no clue about the time and effort that goes into a quilt, and most people want high quality for low dollars. If you do decide to go ahead and do it, I would show him pictures of patterns that you feel comfortable doing, and make him choose which one he wants. Make sure to follow all the other tips given, and if you do it, post pictures. Good luck, whatever you choose.