I'm in the process of designing and developing a database to sit behind a web application I'm building, it's definitely the most complex I have ever built and I am struggling with the first form due to the huge amount of information being stored from it. (Huge for me anyway!)
Here is a screenshot of the first few tables so far:

I was hoping someone could explain to me why I can't create a Primary-Foreign key relation between all the tables with intDwelling_id? It just won't let me do it.
The way i have designed it is that each project can have a dwelling, each dwelling can have multiple windows/doors/floors. So there will be maybe a dwelling with 4 floors (unique IDs for each), but they are all linked to ONE intDwelling_id.
If this doesn't make sense, please ask me to elaborate. But I'm really stuck with this design so far!
