Foundation, col A - ch2, sl st into 1st ch to make a ring.
Rnd 1 - ch3 (counts as 1dc), 2dc, ch2, *3dc, ch2, rpt from * 3 times, sl st into ch-3 to join, cut yarn, fasten off and wave in ends. [12dc, 4 x ch-2 sps]
Rnd 2, col B - sl st yarn col B into any corner ch-2 sp, ch3 (count as 1 dc), 2dc, ch2, 3dc in same sp as ch-3, ch1, *(3dc, ch2, 3dc) in next ch-2 sp, ch1, rpt from * 3 times, sl st into top of ch-3 to join, cut yarn, fasten off, and weave in ends. [24dc, 4 x ch-2 sps, 4 x ch-1 sps]
Rnd 3, col C - sl st yarn col C into any corner ch-2 sp, ch3 (count as 1dc), 2dc, ch2, 3dc in same space as ch-3, ch1, 3dc in ch-1 sp, ch1, * (3dc, ch2, 3dc) in next ch-2 sp, ch1, 3dc in next ch-1 sp, ch1, rpt from * 3 times, sl st into top of ch-3 to join, cut yarn, fasten off and weave in ends. [36dc, 4 x ch-2 sps, 8 x ch-1 sps]
Rnd 4, col B - sl st yarn col B into any corner ch-2 sp, ch3 (count as 1dc), 2dc, ch2, 3dc in same space as ch-3, ch1, (3dc, ch1) in next 2 ch-1 sps, * (3dc, ch2, 3dc) in next ch-2 sp, ch1, (3dc, ch1) in next 2 ch-1 sps, ch1, rpt from * 3 times, sl st into top of ch-3 to join, cut yarn, fasten off and weave in ends. [48dc, 4 x ch-2 sps, 12 x ch-1 sps]
Rnd 5, col A - sl st yarn col A into any ch-2 sp, ch2 (counted as 1hdc), 2hdc in same sp as ch-2, work around the edge of the square making 1hdc in each st, 1hdc in each ch-1 sp, 3hdc in ch-2 sps, sl st into ch-3 to join, cut yarn, fasten off and weave in ends. [72hdc]
Finishing - If necessary block the squares to ensure that they are of an even size and shape to make joining easier.