From an article in the Casino Player Magazine ( several years ago) the comp equation for roulette is :
30 ( spins) x .052 game advantage )X $25 (average bet) X 3 hours - $117.00 .
The pit boss might give you a comp of $ 60.00.
Subject to change and locality. But a good guide line. Make use of your players card.
Comps are very dependent on location. Vegas is stingy but Reno joints are generally very generous with the comp, hey hey.