Odd, I don't think the photo is of the pattern.

Anyway, you must have figured out that each repeat is 15 stitches, so you'll need a multiple of 15 chain stitches for your foundation row plus one more for the turning ch and a few more for miscounts.

Baby afghans are what, 30" to 36" on a side? So you'll need a foundation chain at least 30" long to make a blanket without ripples. With ripples, make the chain almost half again as long; a little less than 45" should make a 30" wide baby afghan and 54" for a 36" width.

So make a long chain then work the first row of the afghan. When you've completed a few repeats and think it's wide enough, lay it down on the floor or the bed in a zig zag to see if it's wide enough. Yes? Good! Chain 1 and turn. You're on your way.

Another comment - notice the holes on both the zigs and the zags in the photo? The pattern, as written, will not turn out that way. Only the valley zags, "skip 2 single crochets," will have holes. The peak zags, "3 single crochets in next single crochet," will not. If you "single crochet, chain 1, single crochet in next chain 1," you'll have little holes. Neither is better, but the photo is misleading. Doubly misleading, because the photo shows double crochet stitches. Oops, a pun. The colors in the photo are very pretty.

Hmm, second thoughts - since single crochet is a short stitch, "skip 2 single crochets" may produce negligible holes so "3 single crochets in next single crochet" will match the valley. Only way to know for sure is to crochet up a sample.

Good luck to you.

Ignore my comments about holes. I just came across the same pattern stitch in a Harmony Guide but with a shorter leg on each zig. It's a multiple of 11 sts. No holes shown in the photo.