You can easily buy the Rome Bus ticket in any tobacco shop (tabaccheria), any small kiosk with magazines and newspapers, in many local bars or in the special ticket machine located in all metro stops for the cost of 1.50 euro. Rome public buses run from 5.30 am to midnight daily. There are also many night buses that function throughout the city. This kind of transport is convenient despite the fact that Roman buses are late in most cases or sometimes don’t arrive at all.
Moreover, bus tickets have a feature that you can also use them for trams and metro. In case with the metro, you can use your ticket only once, while with buses and trams your ticket is valid for 90 minutes after the validation. Don’t forget to validate your ticket in the yellow machine inside buses and trams! If ATAC worker catches you without the ticket or even with the ticket which is not validated, the fine is 50 euro. Read more about buses in Rome here