Originally posted by MythN7:

Originally posted by _I_:

you can put tar on platforms to prevent weather/rain damage

so i could tar a regular flat floor board and use it as a modern roof?

It's not "putting tar on", you use tar in order to craft new build pieces. You can craft darkwood beams (like regular beams) and the same roof pieces as normal but tarred. I believe the only difference is they look aesthetically different.