def mainProjects = [':sdk_ad_casual', ':sdk_ad_base',  ':sdk_ad_framework', ':sdk_ad_google', ':sdk_ad_self']

task delAssets(){
    delete('build/assets')
    delete('build/libs')
}

task createAssets(type: Jar, dependsOn: delAssets){
    baseName 'build/assets/assets'

    project(':sdk_ad_base').fileTree('src/main/java/assets').each{
        from it.getPath() into 'assets'
    }

from ".." // I assume that you add another path here not ".."
}

task oneJar( type: Jar , dependsOn: mainProjects.collect{ it+":build"}) {
    baseName = 'build/libs/sdk_ad'
    from files(mainProjects.collect{
        zipTree(project(it).file("build/intermediates/bundles/release/classes.jar"))
    })
    from zipTree('build/assets/assets.jar') exclude 'assets/META-INF/**'
}

oneJar {}.dependsOn createAssets