How to build OpenWrt for several devices?

I have 3 different devices with openwrt. I has build openwrt from sources with my patches for each one. But I have 3 different source folders with full openwrt source pack. Each one generate separate bin directory. How I can make to generate one union directory?
For packages and target in same place.

You could use ./scripts/env - I am building for four different (sub)architectures (ath79, x86, ipq40xx and mt7621) all in one source tree. Works beautifully.


you can set the same bin directory for all three, from the make menuconfig select "Advanced configuration options for developers", press Space bar to activate it (will show a * in the brackets), then press enter to get in its menu.

There, at second line press enter to write the path for binary folder
Also in the line under it you can write the path for the download folder so you can avoid downloading multiple times the same thing if you are just cross-compiling for different targets.