Ok, I got it working. Actually I use Home Designer Architectural so I cannot export 3D stuff but I know someone who can.
In Chief create a "Perspective Full Overview." 3D->Create Perspective View->Perspective Full Overview
Then Export to dae format (3D Collada). File->Export->Export 3D COLLADA Model (DAE)
Now backup the entire plan to a zip file. File->Backup Entire Plan->Backup Plan Files and all Referenced Files. Also Check "Send Backup Files to Zip Archive"
Extract the zip files to a folder, copy in the dae file you exported.
Open Unity. Go to Assets, Materials, and copy all your files from the Backup Plan archive here, except the .plan and .dae file.
Copy the dae file to the Assets directory.
Finally click the dae file in Unity and under Materials, ensure Import Materials is checked and these to options are selected: Material Naming: By Base Texture Name; Material Search: Recursive-Lookup.
Now you should be able to copy your dae file to the Unity Scene window and see your plan including textures.