CAD tool development using c#

Question

I am c# programmer,i want to develop a CAD like tool(2D or 3D) for drawing(Lines,circle,polygon,cubes).i don't know how to start,can any one help me so that ill start my project,deadline is may.any reference or links so that ill start as soon as possible plz..
features:
1)user will draw rooms of a house for example using the GUI provided by the tool which we are developing.
2)event handling for data  collection (optional).