Hey Ixe_Zitin,
First you need to decide what aircraft you want to built. Once you've got that sorted, you need to look for line drawings of that aircraft.
A good place to start is right here at SimV in the Design Resources Section...
http://www.simviation.com/designresources.htmYou can also have a look at...
http://www.airwar.ru/other/drawe.htmlOnce you've found the drawings for the aircraft, you need to cut and paste the bitmap as mentioned on the Gmax Tutorial so that that CoG (Center of Gravity) on the aircraft is in the middle of the bitmap.
Also have a look at this site...
http://dfast.gmaxsupport.com/web/templates.htmRegards,
Stratobat