Need Help - Like UML Tool

UML is not a tool. I think you are talking about developing a UML designer and developing a tool like UML designer in .NET will require extensive experience of GDI+. Since drawing requires a good experise it will have to be done by an Architect level developer. Your client should think about using Visual Studio or other cheap tools. If they want to get it developed themselves, it wont be a month or two job.  Again, it depends on how much functionality they want. Look into GDI+ section of C# Corner and will give you some idea on drawing graphics objects etc.