When I check my baby’s back and chest to see if he is warm enough they are very different. Usually, because my baby rolls onto his tummy in the night, his chest is warm and his back is cold. Does this mean he is cold or warm?

What you are describing may not be unusual. Temperature of a baby is not always constant & often the tummy will feel warmer if baby is sleeping on tummy.

How old is your baby?
How long has your baby been rolling?
Is he in a cot or still in a bassinet?
Are you still swaddling/wrapping him or is he in a sleeping bag? (with arms out)
https://rednose.org.au/article/how-much-bedding-does-baby-need

If your baby is settling ok, sleeping ok (for age) & not waking at unusual times during sleep (especially in colder months) he is probably warm enough.
Can you discuss this more specifically with your Maternal or Child Health Nurse?