I think you have to tell us how the microwave will be mounted.... a shelf, bottom of cabinet, built in to cabinet.... ?

Built in over the range type microwaves are hooked on to a bracket which is mounted on the wall. If you tile first, you have to find your studs and drill through your tile to mount the bracket. Not impossible, but certainly a little harder.

Most OTR microwaves sit proud of the upper cabinets by a couple inches. Yours would be a couple inches + the thickness of the tile. I wouldn't think that would be particularly noticeable.

I generally like to install my microwave and then tile up to the bottom of it.

Thanks everyone. It is not an over-the-range microwave--it's being mounted under an upper cabinet like this:

I'd like the option of someday ditching the microwave and using the space as a shelf, otherwise I'd just tile up to the bottom of it.

The builder was clueless, but the tile contractor was confident that the microwave would fit and he didn't charge extra for the labor/materials used so I okay'd it. Hope it looks okay!