Colosseum build by me in about 3 months, because I also worked on other things. I build it alone. The first blocks of the Colosseum (around 4000 stone blocks) were mined by me. After that I stopped mining my resources, because it would have taken me some more years to finish it. I got inspired by the one in the Godcraft server made by Sounas and Bodydrag and their crew. It doesn't consist of a Hypogeum yet, but this will be one of my future projects.
It has the same dimensions as the one in Rome. The inside is mainly done by my imagination, as well as the entrances to the arena and the emperor seat.
It is my first big project. I will do more projects in the future, that will mainly be roman themed.
I am looking for some experienced builders that want to help me with some of my next projects ;), send me a PM.

The terrain is quite flat, because I'm leveling the area to build a big roman city around the Colosseum.

You can use it in anyway you want, but don;t say that you are the builder because you aren't, if you want to do so, go build your own Colosseum. It is missing the furnishing of the imperial seats and quarters as well as an entrance to it. It also misses a Hypogeum.