We can all help, but we need to know a bit more than that the site will be classifieds. What's your budget? Are you able to code small changes to the theme or does it have to be 100% right? How do you want the homepage to look? How do you want index pages to look? How do you want listings to look?
Before getting suggested can you please elaborate more about how you want your classified website to get designed. Since there clone websites available like happysale.com and carousell.com which are with advanced features. Or just the simple classifieds website to list around the products between seller and buyer,
I think you are looking for a WordPress theme. I suggest you to take a look here to get a list of premium WordPress theme. http://www.webhostingplanguide.com/top-10-premium-parallax-wordpress-themes/
Even if you go for wordpress, try advanced classified system. Just posting free or paid ads are not making money now a days. Let them chat with each other on the apps and website. More your visitors interactive, more the traffic. More the traffic and as you know more money. In case if you are interested you can check carousell.com , happysale.com , wallapop.com, those people are good in interactive buy n sell. If you are looking for such script, click the website linked in my signature.
What kind of a classifieds website you would like to design, Is that a simple website listing are with some advanced features we can expect from happysale clone. I guess those people are good on customization too they can help you with theme integration.