Andy M.
Certified Pretend Chef
If it's a new construction, by all means, get the shrouded hood instead of an overhead microwave/hood. I'm assuming the builder's micro/hood combo does not vent outdoors.
We have a Vent-A-Hood installed in our kitchen.
Over the stove, as part of a vent hood is the WORST PLACE for a microwave. It gathers grease and is overheated by the oven and burners. And you end up with an inferior ventilation system.
Get a good hood vented outdoors and find a patch of counter space for a stand alone microwave. You'll thank me later!