This really has a feel of greatness (exoecially since we are oh-so-obviously- looking up at it. I like how you had the stains (?) ont he front wall because it really gives it a nice touch. Question: Did you draw it in pencil first or with pen straightaway?
About the 'Stains': There are only a few large scale Gothic-Revival structures in the US that use polished marble. So what appears to be stains is actually various colors of local stone used in the construction.
Pencil or Pen- I'll share my process if it will help you out. Just send me a message. Overall, I use a Pen and Ruler. Most of my work is a little looser than this one, but I really got sucked into this one and wanted to show every detail.