Hi, I have never done a top down cardigan pattern but would love to give it a shot? There is a pattern at http://www.cosmicpluto.com/blog/?page_id=397 that I am going to try.
Question is…If I want to add a lace pattern of some sort, how would I incorporate that into the sweater without the sizing being thrown off? and what would be the best lace pattern to try. I am not a really experienced knitter, just an intermediate.
Thank you in advance for your help 
Bev
The yarn required is worsted or heavy worsted so I’m not sure that one would lend itself to lace, but you could still get the effect of openness and lacy-ness by using a simple pattern with YO. Lace patterns are pretty stretchy so the simpler the better so as not to throw the size off.
As always do a swatch so you can see how it work in the pattern.
Thank you for your help. I will look for a pattern with a YO 
One of the easiest lace patterns for lightening up a solid fabric is Purse Stitch.
Here it is in its entirety:
On an even number of stitches,
K1, *yo, p2tog. Repeat from *. End with k1.
Every row is the same.
I’ve used this on the yoke of a worsted weight cotton sweater and it worked out well. But please take Jan’s advice and do a swatch to see how it will look in your yarn.