Working from sketchup pro to Buildsoft diamonds

For a project I’m trying to make a drawing in sketchup pro, exporting this to DXF and then importing it in Buildsoft diamonds.
Buildsoft diamonds has the option to make polylines into planes but sketchup doesn’t work with this type off polylines.

So I found the extension weld, if i use this on a rectangle (only the lines) it creates a polyline. To get the right polyline to export I have to do a right click and select ‘convert to polygon’. Then when I export to dxf and then import in diamonds I get a surface.

The problem starts when I start to work in 3D I make a horizontal polyline and a vertical polyline but when i combine these the ‘weld’ command becomes undone. So when I import that in diamonds I only get seperated lines.

Somebody who knows how I can fix this? Or what I’m doing wrong?