water color quilts are generally made with 2" squares- you can purchase fusable interfacing with a 2" grid on it- you lay the squares onto the fusable side of the interfacing-arranging until you have it right-then press the squares into place- then you fold each (line) of squares right sides together and stitch your 1/4" seam- when you have them all stitched in one direction you turn it, and do the same in the other direction.
quiltsmart is one source for the grid- and they have tutorials- pictures- i will take a picture of one of the blocks i've been working on - front & back tomorrow- and come back to show you-
if you can not find the grid where you are you can pick up a lightweight fusable interfacing and draw the 2" grid lines on it yourself- you can make it any size you want using it- i purchased a bolt (15 yds) of the grid interfacing- then i cut squares- line it up & press the edges together to make it the size i need. watercolor quilts are beautiful and really not as (daunting) as they appear.