S.D.
My girls are almost 8 and 9 1/2. They have shared a room most of their lives. I agree with what others have said - they need their own space for their own stuff. My biggest issue has been bed time. It works best for us for them to go to bed at the same time at night. My older dd thinks she should be able to stay up later, since she is older, but that is too difficult. She ends up waking up earlier in the morning than my younger dd, as she doesnt need as much sleep, and that works well. Last summer we tried putting them in seperate bedrooms. It didn't even last a week - they both missed each other! They often (not on school nights) will sleep together in one bed and miss each other if one is gone at a sleep over. They do fight, like any siblings would, but they are very close and part of that is from sharing a room. I think it is great you are putting them together BEFORE the new baby is born. It will be important for both girls (the one losing her room and the one getting the roommate) to be able to redecorate the bedroom they will be sharing. I would even suggest letting them help redecorate the baby's room. Good luck, they should love it!
S.