There will be no civil record of bith extant if it was a 1856 birth in Roscommon.
Your options are very limited, mainly depending on Church Records but there is a directory from 1856 for Roscommon surviving, Its the Slaters directory of Boyle, castlerea,rlphin roscommon and strokestown, it may list possible father is he had a trade.
Does he come to England later? I only ask as there is an Owen Grogan on the UK census for 1861, 1871, 1881 etc etc - in the North of England (and listed as born in Ireland) - you probably already know this though
Hi La Diva. Many thanks for the trouble you are taking. It is possible he was baptised in 1857. He was a catholic and thats all I have at the moment.
Merry Christmas to you and yours