You should try Classipress from Appthemes. I've worked with it for a while, my task was to develop payment gateways for local banks and SMS providers. My experience with it was pretty satisfying, the site runs smoothly for 18 months and is a stable source of income for its owner.
If you are not tied to Wordpress.. and don't mind paying a few dollars. Have a look at the classifieds from Fynax. IMO, a dedicated platform is always better than a plugin or extension. I have used a few of the scripts from them and they rock. Good support "very important".! Bit of a learning curve, but does it's job well. http://www.flynax.com/ If you DO WANT to use Wordpress, and don't mind learning.. make your own.."whatever you want"! WP-Types - paid http://wp-types.com/ PODS - free http://pods.io/ I prefer WP-Types. Learning either of the above mentioned will pay off in the long run. You can literally smoke out a custom site with front and back content types in no time. Best of luck. Regards, friedbass.
Could you please describe your needs? What kind of classifieds website are you going to create? Here you can find more info about classified software and the key points to pay attention to in search of the right script. http://www.worksforweb.com/publications/how-to-choose-and-buy-the-best-classified-script/
You don't have to develop anything by yourself. Just use all features of this script. Easy to use Very Customizable Professional features http://classifieds.nikipink.com/ Good luck ♥
There are many very good classified themes for WordPress. Depending on the nature of your site and overall project needs, you may require something that integrates with an ecommerce platform. One theme I used for a recent client project that has a lot of great features and functionality right out of the box: http://themeforest.net/item/flatads-classified-adswordpress-theme/7157644 Also search themeforest for "classified" to see their variety of available theme options.