I'll second what Will S says. A serger by itself will not be a good machine for kite building unless you plan on all one piece kites with the only sewing around the edges. Older Pfaffs with IDT are good machine choices.
Look for 1222, 1222E, 1171, 1371, 1471, 1472, 1473, or 1475 machines. The 1222 series is all mechanical, the 1171 picks up some nice electronic features, needle down, sew slow, low bobbin indicator and is still a mechanical machine. I think the 1371 is still mechanical with a few more whistles, the 14XX series are still basically mechanical but have on board computer boards to drive everything.
Any machine with proper setting, straight and ZZ stitches will make a great kite. I started with a couple of Singers, still have one of them (it's the wife's) and a 1222 and 1171 (they're mine
and only sew kite related items)