How to implement Builder pattern in Kotlin?

Hi I am a newbie in the Kotlin world. I like what I see so far and started to think to convert some of our libraries we use in our application from Java to Kotlin.

These libraries are full of Pojos with setters, getters and Builder classes. Now I have googled to find what is the best way to implement Builders in Kotlin but no success.

2nd Update: The question is how to write a Builder design-pattern for a simple pojo with some parameters in Kotlin? The code below is my attempt by writing java code and then using the eclipse-kotlin-plugin to convert to Kotlin.

class Car private constructor(builder:Car.Builder) {
    var model:String? = null
    var year:Int = 0
    init {
        this.model = builder.model
        this.year = builder.year
    }
    companion object Builder {
        var model:String? = null
        private set

        var year:Int = 0
        private set

        fun model(model:String):Builder {
            this.model = model
            return this
        }
        fun year(year:Int):Builder {
            this.year = year
            return this
        }
        fun build():Car {
            val car = Car(this)
            return car
        }
    }
}