Our baby is 5 months and is able to roll from back to tummy, but not tummy to back. Recently he has been rolling on his tummy during his sleep and we have been moving him onto his back. However, he will keep rolling back onto his tummy and we have been waking up every hour to move him. Sometimes he will be face down, other times his face will be turned sideways while on his tummy. Is it ok for him to sleep on his tummy or should we continue to turn him onto his back? He is sleeping in his cot, with a sleep bag (arms out). We do cover his hands with the built in hand cover from his bonds wondersuit as he likes to suck his hands.

Most babies will be rolling over by 4- 5 months…...some earlier, some later.                             
This is normal as babies grow & become stronger.
Many babies then prefer to sleep on their tummy or side.
This is not something that needs to be stopped. It is important to make his environment as safe as possible.

It is important that you have moved him to his cot & that he has his arms free - baby needs his arms free & the space of a cot to roll well.
Ensure his mattress is firm, flat & well-fitting.
How does he go with tummy time when awake? - increasing this will help him to build up his upper body strength for rolling.
Always continue to place baby on back for sleep.

Waking every hour to turn him back is not sustainable, but if you see him on his tummy when you are awake, try turning him back but he will soon show you he can roll both ways or move around the cot & then he can be left to find his position of comfort - but always place him on his back for sleep.

Have a read of the Red Nose information (link below) now that he is rolling . 

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
**At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
*By this stage it is not necessary to wake during the night to turn baby over to the back position
Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over