Crochet an odd number of chains.
In the second chain from the hook, sc
Dc in the next stitch
Continue sc then dc, ending the row with a dc.
Ch 1 and turn
Repeat the sc then dc across (you’ll sc into a dc below, and dc into a sc below).
I started with 31 chains, and did enough rows to make a square. It’s a little bigger than I wanted, so the next time I might start with 25 or 27 chains. Or maybe not!