By default all \wwwroot folders are already configured as application directories. This allows your asp.net applications to run from \wwwroot\
If you require to setup a virtual directory that is outside of the hosting folder you can use virtual directories option, if you need the folder to run as an application on iits own you can use the virtual application option.
The option to do this is as follows :
1) Login to SolidCp
2) Click Websites, select the website you want to edit.
3) Click the Virtual Dir / Application Dir tab
4) use the appropriate option need for your requirements.