As for the roof, it has to many details for sure.
I bet your roof will never been seen from such a close distance to justify that ammount of detail.
Also very long thin triangles can have a bigger impact on performance, so don't use these unless it's unavoidable.
This would be the perfect oportunity for you to learn something about creating normalmaps.
Just a quick example on how well normalmaps work for these kind of prop:
Ofc. you will add more details.
For things like the small stoneblock details, i wouldn't do them as seperated blocks with chamferen edges at all.
Example:
From a little distace there won't be any noticable difference esecially with a good diffuse and AO added.
A little Update:
A sculpted highpoly stone in the front, a row of lowpoly stones with baked texture in the back.
If these models were placed somewhere the player can get very close to, i'd add a chamfered edge to the lowpoly, too.
But since the rooftop is usualy only seen from distance, a simple box will be enough.
Just in case you wanna try sculpting, too. This is the mesh i used as a base to sculpt:
For sculpting apps without dynamic remesh feature, it's important to have a basemesh with
equal quad resolution across the surfaces.