I do not think what you want to accomplish should be to hard I see maybe 3 possible ways of doing it one is perhaps

Medieval Tower with Wall Factory I thought of this one first because the Wall Factory add on is already part of Blender and might have to use a bit of imganation and doing it as sections to achieve the look you

This is a full Tutorial on making the Colosseum in blender longer tutorial but nice detailed process

Creating a 3D Arena using Blender 2.81a Shorter video but for getting a concept idea as to how difficult which again I do not think it would be

Hope these help

Lobo3433

Blender Maya & 3D Forum Moderator

Renderosity Blender 3D Facebook Page

Forum: Blender

Subject: small amphitheater