Creating a walkthrough using Revit is easy after completion of building design.
You also can create a walkthrough as bellow.
Go to the Floor plan of the Project. (Floor plan can be chosen according to the eye hight of your camera.)
Then find the walkthrough on the View tab.
Then you can Draw the path you want to take the camera.
Click on edit walkthrough and then you can rotate your camera to adjust the view.
Then click walkthrough on Project Browser to open the view.
Then again click edit walkthrough, set the frame number 1 and then you can play it to check whether all the thing is according to your desire.
Finally, you can export the video by File-Export-Image and Animation-Walkthrough.
Watch this tutorial and get a clear idea of creating a walkthrough using Revit.