Archway help required

I was going to use on my layout area some pre-made brick or stonewall sections on the layout where the raised area is going to go on the left handside of the layout but after struggling to get hold of anything that will remotely do the job. Whilst in bed last night I thought to myself why not use the area I have built up and cut some archways into the foam and put some photo's or pictures of shop fronts scaled down into the arches. I know I'm going to have to add some kind of wall to the top of the edge to make it look real down the length of it either that or add some kind of fence either metal chainlink or wooden as you would expect to seperate the ordinary joe public from network rail property.

The problem I have is that with me living in Thornaby I'm kinda stuck as to what this kind of archways look like and also the sizes of stone or brick used and also getting it looking to scale in the foam I've used.

I'm also not sure that because when I have skimmed over the grout and it's not a perfect finish would the roughness of the skimming add to the archway realism or would I really need to smooth it down before scoring the brickwork into the plaster.

Anyone who has any ideas of what size I really need to make the stonework to be able to make the archways look good and real enough are welcome.

This is the area I am on about which I am thinking of using to make the archway itself.