I have made 2 quilts for raffles, ( and I agree raffles will bring in more money). One of them was a queen size quilt and it was a green and brown tube quilt, easy to put together. The other one was a twin, simple red and blue and white star quilt. I was worried that they would not buy as many tickets if it was just a twin, but it brought over $375.00. The queen brought in around 350.00. I realized through this is that people don't buy or bid on a quilt due to the size. If they like the colors and pattern then they buy the tickets. I would not make a big one, just because it is expensive to make and you can make just as much with a smaller quilt. You also need to be careful with color selection and a more neutral color palette would probably be received better.
Best of luck, you have plenty of time to make one. Keep it simple is my advice, Beth