I can't build my project .

here is my build script :

buildscript {
repositories {
maven {
url = "http://maven.bluexin.be/repository/snapshots/"
}
maven {
name = "ilexiconn"
url = "https://maven.mcmoddev.com"
}
jcenter()
maven { url = "http://files.minecraftforge.net/maven" }
}
dependencies {
classpath 'net.minecraftforge.gradle:ForgeGradle:2.3-SNAPSHOT'
compile "net.ilexiconn:llibrary:1.7.14-1.12.2"
}
}

You've put the LLibrary maven and dependency in your buildscript block, they need to go outside of that on their own like:

buildscript {
    repositories {
        jcenter()
        maven { url = "http://files.minecraftforge.net/maven" }
    }
    dependencies {
        classpath 'net.minecraftforge.gradle:ForgeGradle:2.3-SNAPSHOT'
    }
}

repositories {
    maven { url = "https://maven.mcmoddev.com" }
}

dependencies {
    compile "net.ilexiconn:llibrary:1.7.14-1.12.2"
}