How do i, in Autocad 2010 3d, make a cylinder that is hollow.
thank you.

Draw circle with the od that you want, extrude to length.  Now there are 2 ways to hollow it out, most efficient is shell command.  The other one is to draw another circle with the id you want the inside to be, extrude that to same length and use the subtract command.
 
The 3D help is quite usefull.....

or you could draw two circles and just extrude the in-between space, then its already hollow.
 
and help sux!!