You can use a roast in the following ways:

a buffet lunch
to supplement lunch / dinner and or for additional guests
for brunch for the morning after the wedding

Each wedding is different so the following questions may help:

How many adult guests?
How many children?
Where is the venue?
What is the date / time of the wedding?

Call Tommy on 086 863 0757 so he can discuss your requirements and provide you with suggestions and a quote.