MyBB Community Forums

i need a theme that lets you post lots of ads on website

You can just add the ads yourself into any theme. You won't fine an "ad compatible" theme, you just need to find where you want it, and insert the code you desire. I would recommend you use MyAdvertisements for ad management, and add variables wherever you want ads to appear (instructions included with the plugin). Feel free to PM me if you need help.

Unlike WordPress, I have not seen any theme with Ads support boxes built in for MyBB. There is a plugin which allows you to add advertisements on popular locations. Other than that, you are on your own ?