According to this cordova guide , cordova-android versions 6.x.x does support 16-26 Android Api Level. So it is supposed to build a cordova project with api level 20, if specified this way.
Even though, I'm not being able to build a cordova project specifying my cdvBuildToolsVersion to 20 at build time.
Gradle build tasks warns me like this:
"WARNING: The specified Android SDK Build Tools version (20.0.0) is ignored, as it is below the minimum supported version (26.0.2) for Android Gradle Plugin 3.0.0.
Android SDK Build Tools 26.0.2 will be used."
Steps to reproduce:
$ export ORG_GRADLE_PROJECT_cdvBuildToolsVersion=20
$ cordova build android