How to design mobile Gantry Crane ?

Hi

I have assignment to design mobile gantry crane in staad pro

But i don't even know how to start it

Can anybody help me ? I need some reference

I use staad pro v8i

if you have an example design of gantry crane in staad pro, please send to my email address shazata8@gmail.com

Thank you so much

best regard,

Nurin Shabrina