The first question you need to ask yourself is, what is the Fire Rating on the floor or Roof. Based on the fire rating requirement, then you can start picking and chosing. The second question is do you need to use Light Weight Concrete since the latter can improve the fire rating requirement.
It sounds like you are designing an office building; therefore, I will give some hints accordingly.
1) The typical fire rating is 2 Hours.
2) For 2 Hour FR, you can either use 3" or 2" Metal Deck with 3.25" Lightweight Concrete Fill (6.25" or 5.25" Total). , or 3" or 2" Metal Deck with 4.50" Normal Weight Concrete (7.5" or 6.50" Total).
3) Typical Construction is Steel Beams at the Floors (not Open Web Joists) and Open Web Joists or Steel Beams at the roof if there is no MEP penthouse.
4) for 30 foot x 30 foot bays at the floors, space your Beams 10 feet appart and stay with 3" 20 GA. metal deck, 3.25" Lightweight Concrete (Total 6.25"). I like to maintain 4.5Hz minimum natural frequency on the composite floor system. Design the Beams as Partially Composite and do not load the beam with too many studs to make it fully composite.
5) The Roof will not need concrete on metal deck if there are few Lightweight RTU's on the roof, in this case you may use Open Web Joists say 2 feet on center with a standard roof metal deck.