Hey everyone! 
I was just exploring Sketchup and ended up building a bridge with a stone texture.
In order to import in Unity, I had to take the following considerations:
• First, as I wanted Unity to recognize the texture, I saved the file in the format .dae and then created a folder in the Assets folder where I copied the .dae file and the folder with the texture.
• Secondly, as @vcard advised, in order for the avatar to not cross the walls, one needs to take care of the colliders. Now the avatar will be able to walk under the arcs of the bridge, but if it touches the wall it won't be able to cross them.
• Last, but not least, I had to take care of the scale, defining the size accordingly to my goals.
The bridge was already imported and the virtual Gonçalo was testing it. Everything is working as expected:
If you feel like testing it, press this hyperlink.
In the next couple of days I will explore Blender, a more powerful 3D modeling software.
I still didn't update my portfolio, however tomorrow you will be able to see the Sketchup model and the import on Unity. In the mean time, if you feel like getting in touch with my other projects: access my porfolio here.
Best regards,