OpenWrt image builder

Hey, Can somebody guide me in applying a downloaded patch to the openwrt while compiling. I've downloaded the patch but unable to write directory where to place it. Somebody please help.

To my knowledge, patches can't be applied with the image builder. It is meant for cooking up the firmware quickly from already compiled components.

You need to use the full toolchain if you want to apply patches.
https://wiki.openwrt.org/about/toolchain

But I am able to paste the patch into its root files in image builder too.

Sorry for wrong info... I am using toolchain builder only and unable to apply patch with it.