I bought some lovely soft NZ merino recently and knew the exact top I was wanting to make. Of course I didn't have the exact pattern so modified one I already had, McCalls M4517.
I made the plain round neck top with long sleeves. I then set about constructing the ruffle. I cut a piece of merino approximately 120cm long by 15cm and folded it in half wrong sides together and sewed each end. I then turned it the right way out and serged the tube closed, and then ran a gathering stitch through to create the ruffle.
Starting where I wanted the ruffle to finish I then placed the ruffle on the top fiddling until I got the placement right. Once happy, I pinned it in place and marked with tailors chalk the line as it would have to moved around a bit to sew.
To stitch the ruffle in place I started at the bottom row, holding the other rows out of the way and stitched the row in place. Each row was stitched individually.
I don't normally sew knit garments having had some bad experiences in the past but this one sewed up nicely with none of the puckering dramas I have had in the past. I sewed most of it with my serger and the seams under stress with a stretch stitch. I also reinforced the shoulder seam with ribbon. After this experience I may sew some more knit garments soon, I especially love the Merino it was lovely to sew and is toasty warm and comfy to wear. Perhaps a bright colour for the next garment, I seem to be on a black theme right now - blame Winter!