That's exactly why I don't like BuildForge. It's a great cross platform, multiple host orchestrator but it doesn't really "build" anything. I spent several years at a company where we had around 800 projects on one server and another 800 on another. We found that if we wrote all of our build steps into BuildForge that we'd kill the database. So instead we had a common library that did most of the work by calling out to NAnt. MSBuild would have been a good choice also but at the time NAnt was more mature.
We ran 100,000 build a year on 60 virtual machines. We had a build step that talked to the VSphere server to reset the VM, wait for it to come back online and then run the build on it.
I also worked for another company that used AStarTeam for source control and BuildForge for builds. I stood up a TFS server and write a Get extension to pull code from StarTeam. I then created BuildForge projects that wrapped the TFS build. As far as the developers knew they will still using ST and BF but in reality I was getting all the Workflow/MSBuild capabilities of TFS with the possibility of them moving the source over one day and being all TFS.
So ya, there is no one tutorial for .NET on BF because it's all on how you want to do it. Perl, PowerShell, NAnt, MSBuild et al.