To make the circle, get a large paper table cloth and spread it out on the floor. Get a pencil and attach it to a long string (1/2 the desired diameter of the circle - the radius, I guess). then anchor it to a spot in the center of the paper, stretch out and keeping the center in place, draw with the pencil. Kind of like the compasses we used in school to draw circles for geometry. It is like when a dog is on a rope anchored in the grounds and can only go in circles. lol
Once you have the paper circle, you can cut sections...you would have to add 1/4 inch to each side of the piece of circle (arc) for the seam allowance to stitch the different colors together. Hope this all makes sense.
Sorry for your loss, I am sure you have a lot of wonderful memories for the time you spent together before his illness, rejoice in them!