The dimensions required are entirely dependant upon which material you select.
This model is designed for FUD. http://shpws.me/lmmj Some of the walls are as thin as 0.7mm, and the gaps are only 0.1mm.
The cab and boom are both fully movable. The cab in particular uses almost exactly the same cross-section as your diagram shows.. just much, much smaller.
On each of the Material Pages you will find a "Clearance" value that tells you how much clearance you must allow to have movable parts.Patience, Persistance, Politeness - the 3Ps will help us get us to Perfect Printed Products