If you are going to write it after the 53 man roster is set, I would consider writing about the 2015 draft picks and who made the roster and who is expected to contribute as rookies.
Keep in mind that I am a big time draftnik and I never get tired of reading about Dallas draft picks... particularly when they're like Gregory, Wilson, and Collins and were steals for where they were drafted.
You could maybe touch on how it appears like Dallas has, for the second year in a row, hit on a little known 4th round linebacker from the Big ten. Wilson is looking like a really good player.
Maybe touch on the versatility of the players Dallas has picked. Byron Jones can play outside CB, slot CB or safety. Damien Wilson can play all 3 LB spots. Collins could play tackle or guard.
If Whitehead makes the 53, you could maybe talk about how Dallas has yet another UDFA who is a good player added to Cole Beasley, Romo, Leary, and even technically Collins if you want to count him.
Anyway, that is just a few ideas and really, you can't go wrong talking about rookies/draft picks.
My advice would be to figure out what excites you about this team and go in that direction. Find something that you get so excited about that you want to tell everyone about and then... start typing and tell us.