Currently it is not good idea to add a new layout in our plugin as it won’t work after the update. So i suggest you here to customize one of them. For that, please copy the layout to your wordpress theme from Wp Masonry > Layouts. After that you will get new location of the layout and you can edit from that location as per needed.
PS : Thanks Johan for taking time to reply in this forum. I really appreciate it. 🙂