When implementing you own struct you should take into consideration the following:

• Use structs when you intend to create a great many of them
• structs should be small. Large structs (i.e. structs with many fields) would lead to poor performance, since structs are copied each time.
• Use structs when you require high density memory collections.  Structs have have a much simpler memory layout and offer excellent memory density and lack of overhead
• Override structs Equals(…) method and implement IEquitable<T> interface to  avoid boxing.
• Overload == and != operators
• Override GetHashCode method.
• structs should almost always be immutable. Actually I’ll go further and say always. Mutable structs could lead to confusion if declared as readonly. Any modifications to a mutable readonly struct will be ignored, making it a very difficult bug to spot.

Structs have also got their own limitations. Since they don’t have an object header, you cannot for example use a lock(…) on a struct since this  will result on compile time error. However Monitor.Enter(…) accepts any object, structs included, thus leading to a bug. The value  of the struct will be boxed each time and that would be equivalent to having no lock at all!