Hi Steven,
I would suggest copying an entire sample osdesign, starting from the top level (the directory where the .sln file is located) and use that as a starting point. You can modify the osdesign name/path by editing the .sln workspace file and the .pbxml project file.
If you want to start from scratch however, you can go ahead and create a New Project in Visual Studio, and optionally use the wizard to put something together.
The BSP may require certain OS features to be present, but looking in the quick start guide (A8 02.30.00) I don't see these requirements documented, so your best bet probably is to just select the same Catalog Items that you see in the sample osdesigns, and then once the build succeeds you can start removing features you don't need.
If you prefer a more systematic approach to selecting OS features, open the .pbxml file from the sample osdesign in a text editor and work through the list of sysgen_* variables that you see. Open your custom osdesign in Platform Builder, and in the Catalog Items View you can search for each sysgen to make sure it is included.
Or you could just post the build errors you are seeing - maybe someone will be able to help.
Best regards,
Carsten