Devendra Badgujar
Ansys Employee

Hi SandorToaso

I would recommend copying and pasting the desired surface. You can then use the Pull command (No Merge ) to create a thickened solid beginning with the duplicated face. Then you just merge them back to make one solid. 

I think you would also want the walls below the highlighted ones shown in the image to be thick, that might require manual construction with using Blend tool with respective guide curves, then basically pulling it. 

Let me know if this helps.