It depends on what the rest of the house looks like. New tile or classic wood trim are both possibilities.

Take Joseph's advice...removal of tiles / repair of walls / install of wood will cost much more than solid surfacing overlay.

You won't have the space to install something over the tile, you'll be over the window height ... do it right and remove the tile before anything else is installed there.

tiles very nice,why not let them be?

"You won't have the space to install something over the tile, you'll be over the window height..."

You can tell that from the picture?

I'm rarely a fan of demolition, especially of apparent original fabric, unless it's absolutely necessary. Someday someone may be delighted to pull the solid surface sills, scrape off the silicone, and appreciate those tile. Never gonna happen with your method.

Are you only wanting to get rid of the

If you're intending to replace a 54" window in a 54" vertical space, you cannot add even one inch atop the existing tiles to do that.

If you're replacing the window, you could opt for a shorter window and have the space filled in the thickness of the difference with a new treated wood windowsill atop the older one.

If you are replacing the windows, I suggest that you have the pro that will be replacing your windows also replace your window sills -- and remove the tiles rather than try to cover them. (But do save as many of them unbroken that you can for a DIY project for your patio later.)

Our house is mid century modern in style, more on the modern side. We aren't replacing windows. One option is to just take off the tile and leave no sill other then the original brick. There is one window in the house like this and it looks fine. May do a test on one high bathroom window to see how it goes. Like the idea of going over the tile but also am not sure there is space.