Gothic architecture, especially cathedrals was based on the idea of “enlightenment” and reaching towards the heavens. On the exterior facade, make sure to add a lot of vertical lines and stretched out proportions. Pointed arches are a neccessity as well. Also, for the most part, gothic cathedrals are layed out in a cross shape. I am assuming that the one end with the two towers is going to be the front of the cathedral. There is typically 3 doors at that end as well. One main door int he center which is usually larger, and a smaller door on wither side. I would suggest at the other end creating the remaining “arms” of the cross shape. Gothic cathedrals are very ornate with a lot of little minute details. there are a lot of little chambers and rooms. Gargoyles are also necessary. They were originally designed to “scare off evil spirits” and also were functional to direct water from the roofs. There are several forms of gothic architecture, my personal favorite is “perpendicular gothic.” For an example, look at Salisbury Cathedral. i am a huge fan of gothic architecture, so if you have any questions dont hesitate to ask. I would be right with you modelling a cathedral if it not for two minor things…talent and ability.
by the way, keep up the amazing work. I am VERY impressed with the modelling quality thus far.