Hi there Laurent.

Listen, it's not really going to be possible to answer the question without knowing a few things. for starters

Which Modelling application are you using?

What's the gothic classroom going to be used for when its done?

Have you designed it yet? Made any drawings or sketches to work from? Do you have any reference pictures or photographs to show what you want to do?

For starters there's a good thread over on the Wings forum showing different ways of making Arches and round windows - key elements in gothic architecture, but it is very specific to Wings.

So what are you using?

regards

peejay