Too much depends on what you need the server to do, I suggest bringing in a professional/consultant. Even something as simple as a file server brings up more complex issues; How important are the files on it? Will you need raid10, 5, 6? How important is the server? What if it breaks down, Do you need a reduntant power supplies or a redundant/backup server? What about backups of the server? Do you need a tape controller/drive and lots of tapes? Which kind? Where to store the offsite backups...