That depends mostly one the type of Semi you like best.
The New Mobius International Prostar, would be the best for Accuracy.
Not many of the Older semi's were converted like that.
Unless they have been recently.
Most are Custom built on New chassis.
Sheet styrene is going to be the shell/body of the Home section.
If you wanted Less Sctratchbuilding, you could start with Revell-Of-Germany's Neoplan City Liner Bus.
They Are used as platforms too. More so actually.
Here you would only have to alter as many of the windows as you wish by painting, and confine
most of the scratchbuilding work to the Inside.
Having an MPC/Model-King AMT issue of the Open Road Mini-Motor home kit will help with some interior parts.
But you can also fine 1/2 inch scale Doll house furniture for this.