Is the black cladding wood or timber effect? Black is pretty neutral so I would decide what shade of brick you like first. Would it be possible to visit a brick manufacturer or does your architect have brick slip samples? There are many different colour variations from reddish, more yellow to grey. You need to see samples in the flesh to decide. Its an expensive mistake to make if you get it wrong. Look at as many examples of brick barn conversions as you can first to get an idea. I prefer stone to brick, especially blue lias. I only really like historic brick on period houses.

My first thought was a lovely orange-brown, the more aged the better, although many companies now recreate that aged look with new bricks. Reclaimed bricks are another option. Depends if you want to create an older classic look or not.

Thanks for those! I’ve ordered a sample of the olde coach house x