This guide explains how to use Xamarin.iOS for Visual Studio and a network available Mac as the host for Apple's complier:
It is possible to use an iPad as the networked Apple compliler?
No. You cannot run XCode on an iOS device, therefore it cannot be used as a Xamarin build host. If you do not have a Mac to act as a build host, you can get one in the cloud from something like this or any similar service