Im doing a complete gut out on 4 - 1500 sf units..only leaving one load bearing wall per unit.HO wants a 27' header installed with steal columns...Im thinking of using a 4"x12" Timber beam if I can get a full run...if not I will use 2- 2x12's..the beam will be exposed, but I have 4 units to do like this..3 jacks studs on each side of the beam

..the 2nd floor only supports the flat roof above but all that weight will be on the first floor, the basement has 6' 6x6 posts every 5'...the ceilings in the units are 9'9" what should I space my columns at? Any Ideas???Thanks.