Both approaches show up, and the plan gets driven by where you can put risers. The usual method is to establish wet columns, vertical zones where kitchens and baths from every floor land on top of each other, and punch new stacks down through the slabs at those points. That gives you short horizontal runs, minimal dropped ceiling, and predictable fall. The price is that unit layouts on floor two through eight have to agree with each other, which constrains mix. If the market wants a lot of one bedrooms and your wet columns are spaced for two bedrooms, you either fight the geometry or accept a mix you didn't want.
Horizontal running in a dropped ceiling buys layout freedom and spends head height. On an 11 ft floor to floor with a beam and girder frame you can end up with 8 ft or less clear once you've stacked sanitary above supply above ventilation, and low ceilings show up in rent. Coring is also not free to design around. Post tensioned slabs need GPR scanning and engineer sign off for every penetration, and a slab where you can't core where you want can move a whole floor plan.
Cost effect is mostly indirect. The direct plumbing scope is a known number your estimator can price. What moves cost per unit is the unit count you lose to riser chases, the head height you give up, and the structural work around penetrations. I'd get a plumbing engineer and a structural engineer to sit over the same test fit before the layout is anywhere near final, because reworking a plan after schematic design costs real money.
One item that gets missed alongside drainage is ventilation. Residential needs continuous exhaust from baths and kitchens and makeup air, and a building designed for a central office system rarely has vertical shaft capacity for it. That shaft hunt competes with your wet columns for the same space. Local code specifics on both vary, so confirm with your building official rather than the model code alone.
