Made some more progress. Finally decided to start cutting up some styrene, now that I know where this is going.

Cut and Installed the 3 front cross members and cab mounts.

Cut up the floor and made it mountable onto the cross members mentioned above.

Cut both sides of the driver cab and started cutting out the windows. Note the smaller window is for the sleeper behind the drivers and passengers seats.

Dry fit the two sides and rear part of the drivers cab together with masking tape to get a feel of where this is going.

Front view

Rear/side view

Here's the engine bay with spare wheels on either side. 

Before starting on the roof, I made a cardboard cutout of what it will look like. Needs a lot of tweaking and more cardboard cutouts before I make the final cut.

Happy with the progress. My first time working with styrene   Still a  long way to go.. No rush.