A bit of a tall order without actually seeing how you plan to use the three colours. I drew one up in EQ using only 2 colours with 12" blocks - 7x7 makes an 84x84" square quilt. Now it tells me you will need 11 1/4 yards ( 6yds colour 1 & 5 1/4yds colour 2), so if you plan an even amount of each fabric I would go for 4yds of each. This does not include borders or binding, though there will be an extra 1/4yd of each colour.
Last edited by Gay; 01-20-2019 at 09:34 PM.