Engine dimensions and weight are calculated for each cycle design point if in the program opening window the scope "More..." is selected.
Local Mach numbers (or flow areas) are the design point input data for the main thermodynamic stations. The shape of flow annulus is fixed by selecting reasonable hub-
If a drawing of the engine you want to model is available, then it can be used as background for the drawing of the GasTurb engine geometry. This is very helpful for designing the flow annulus and the disks.
See below a few examples for the geometrical engine design capabilities of GasTurb. Note that all three turbojet drawings are for the same thermodynamic cycle.