I say first off look at many others who have done Ivy (inspiration), and many versions of her like Ame-Comi, the 50's one, and many many more. Choose a style of her you like, or part's of the costume you like. Mash up if you like. Ironman/Poison Ivy mash... Armored Ivy... hmmm, second though maybe I should do that one, or Armored Harley... maybe for Con instead of just Halloween ... Sorry, back to topic... Also look at other ages or genre's, Medevil Ivy, Noir Ivy, or Zombie Ivy. Search engine (or multiple ones) on images is your friend... LOL
Look at the picture of Immerel08 that previous person linked to. Dude did a good job. Other things factor into your costume, such as body type and build. Immerel08 has a pretty well built body and could have gone more a simplistic covering and shown more skin. But he went more military than sexy.
Rule 63 can be fun and also can be scary at times. Seen many well done ones (like Yrlen's hubby's Harley), some fun ones (5 very built hairy guy's did Sailor Moon Scouts (headband, speedo's, boots and gloves)) and seen some really eye bleaching ones.
Bottom line - look for something you really like and want to do, and put your heart into it. If you don't like something it will turn to work and not "feeling" it and you will not have a good time while wearing it.