are there any buildings that you can go to the top of —for example the AT&T building or the Sheraton looking for a tall building for the views
The L & C Building had an observation deck at the top for years, but I believe it closed sometime in the early 2000s.
I think the only way you can get to the top of a tall building is to just ride to the top available floor and look for a window. Unless somebody else knows otherwise, there are no observation decks any more.
The Tennessee Tower has a top floor that is essentially a walking track surrounded by huge windows. You used to have to flash a state ID to get to the elevators, but you might be able to ask at the front desk. This is by far the best vantage point I know of in all of downtown.
The State Capitol allows visitors to go out on the north veranda, which provides a beautiful view looking north towards Bicentennial Mall and also with slight views to the east and west. It's not a high rise, but the building itself still sits a few hundred feet above ground level. Outside of the Davidson Co. Courthouse, there is a 2 story observation deck that provides great views of the river and immediate surrounding area. It also has a little permanent exhibit telling the history of Nashville.Edited: 10 May 2018, 21:02
The observation deck outside the Courthouse that Downola is referring to is on the east side (towards the river) of Public Square Park located on Union between 1st and 3rd Ave. As Downola said, it's a 2-story structure so you only get good views of the park, river, and immediate buildings.
You can go to the L27 Lounge in The Westin. Incredible views.