Hi There! you can use Sketch up. it's a Freeware, easy to learn, 3D image and have specified parameters.

Google sketch up is good. Also easy to learn.

I've only used these to import darwings into AutoCAD, but it looks like they have their own free tools.

http://www.lesker.com/newweb/chambers/chamber_builder_overview.cfm

http://www.lesker.com/newweb/cadregistration/reg_form_secure.cfm

Solid Works.

Solid Works or labview

as @Dennis mentioned, some companies provide 3D models of vacuum components which saves some hours of work. 

Sketchup is nice, but it is also very limited in comparison to 123D from Autodesk which is also free.

Sumit,

In general, if you are designing a chamber from scratch, you are better off talking to the manufacturer. They will recommend a stock 'base' (cylinder, hemisphere) and then you can add ports to your heart's content.

Unless you have a very good understanding of the stresses involved, I would suggest that you don't try to design one completely on your own.