To create a custom attribute for classes , methods or properties you have to create a new class inheriting from System.Attribute This is a sample for a custom attribute class
[AttributeUsageAttribute(AttributeTargets.All,AllowMultiple=true)]
public class Author:System.Attribute 
{ 
     public Author(string name) 
     { 
           this.Name = name;
     } 
     public string Name 
     { 
           get; set; 
     } 
} 
and you can then use it like this 
public class ClassWithCustomAttribute 
{ 
     [Author("Mustafa Refai")]
     //here is the custom attribute 
     public string Property1 
     { 
           get; set; 
     } 
}