Hi I am anlaysing the external flow of a fluid of a rotating object, at the moment i am using the rotating wall method but wish to move on to a transient rotating mesh but i am having problems constructing it in pro-am. I have a stl file of the object with the domain but what i want is a cylinder around the object so i can create a face to put the attach boundaries on. How in pro-am can i create this internal feature?

Try using the PATCH command in prostar. Before that, you'll need to create splines for the cell patch to 'snap on'. Create vertices and rotate them all around to help you draw the splines. The PATC command expects a continuous spline in-betweem neighbouring corners or otherwise your cell patch will just have straight edges.

Easier to go back to your CAD program and then draw a cylindrical surface based on the same coordinate system / part file and then use ProSTAR/AM to import it. Imported geometries overlap.