ab/testing custom goals setup in GA assistance needed

I need you to help me setup GA A/B split testing using a custom goal. I can already setup and run an A/B split test, but need to measure a specific/custom goal. The page that I'm testing sells "doors" and there is a number of doors on the page. The conversion I need set is to measure how many unique page views actually click on a "door" so need to calculate the conversion rate of the page, based on have many click on a door page - and there are 23 doors on a page - so 23 conversion pages to set. Please bid if you fully understand what I'm trying to achieve, or let me know if you have any questions. Thank you Chris.