A prefab map is nice, but it needs more content. If you are going to prefab arches I would suggest making a 'good' arch for each size opening from 4x4 up to like 12x12, then do a few larger arches too. just two arches isnt really a good prefab map. a dozen arches would be a minimum, the more the better.

you should add tons of different types. like those spiral stairs and ladders and normal stairs as well. and fences etc... i will help if ya want