Scaffolding boards make a great building material, they are strong and rough, that means there is a lot of room for a creative finish. You can keep sawmill like patterns and add some nice stain, varnish, whatever you like really.
They are thick, so any project done with these bad boys will be a strong and sturdy piece. Adding some hardware will bring the work to another level, specially if you like the industrial/loft style designs.
As with most of wood work, your imagination is limitless really, one thing is worth looking into-the old, naturally aged scaffolding boards, ones that have taken a fair amount of abuse in their lifetime-that finish made by nature will be hard to replicate really. So if you see some old boards at some construction site-ask if you can have them and go to town baby, make something cool out of them.