Create new empty solution with name Solutoin1. Place this solution into the foldeer C:\Projects\Solution1. Add new solution folder Source into the solution. Right click on the solution folder Source an click "New Project...". Select Class Library project. The location for this new project will be set to C:\Projects\Solution1.
Today, the solution folder names are not added to the preset value of Location of new project, which are added to the solution. If you want to have the solution structure the same with physical location on hard drive, you need to chande Location value. it is easy to make mistake during the project creation and than you have to repair it.
It shold be posible in properties window of the solution folder to choose, if I want to automatically map this folder to the physical folder or not. If i set that i want to do this mapping, than during creation of new projects into the solution folder their location will be preset to the path containing the solution folder names (c:\Projects\Solution1\Source). This settings of the folder shoul be placed into the solution file, so, it should be shared beetwen users using source control.