add = this.form.group({
    buildingNo: [null, [Validators.required]],
    roomNo: [null, [Validators.required]],
    roomResourceType: ['1', [Validators.required]],
    roomBuildAcreage: [null, [Validators.required]],
    roomEquipments: [null, [Validators.required]],
    roomDecorateState: ['1', [Validators.required]],
    roomRentedAcreage: [null, [Validators.required]],
    roomResourceState: ['1', [Validators.required]],
    roomDesc: [null],
  });

现在想验证 roomBuildAcreage必须大于等于roomRentedAcreage 的自定义验证应该怎么写啊

小白求教