Well, english isn't my first language here...
and I wonder if I interpret this pattern correctly
ch3, 6 dc only through the front loop of the first hdc of previous row, *7dc only through the front loop of the next hdc of previous row* rep from *to* all around the row.
Then, ch2, hdc only through the back loop of the hdc of row 1.
Rep the ROUND 2 until it reaches the height you want.
6dc front loop, 7dc front loop in next stitch. Repeat, until the end of round 2.
Ch2, hdc all round in back loop of round 1.