Interesting question. While there are many solution, I would venture that there are no "wrong" ways as long as it works. However, some solutions will be much better than the reast. I would be weary of any answers given without someone first asking for a few more details. To a minor extent is the distance between the buildings. More important is (not all are needed, but could help)
- how many users in each building?
- how many systems in each building?
- server farms? which buildings?
- your question indecates pre-existing networks
-- if so are the same subnets shared between them?
- are there rtrs or swt's in place?
- any other useful info?
- type of platforms?
- type or protocals?
- type of work being done? e-mail, mathmatic calculation? cad? other?
remember, don't give us actual subnet ip's.
I just would't want to mis lead you.
For what is is worth... first network I took over consisted of buildings with multiple networks bridged for connectivity. Performance stunk. But it was a high performance & over utilized nw.
sorry to offer q's and not answers. :-(