The Spanish Tax Agency (AEAT) has published a series of xsd for the new system of Immediate Information Supply (SII) that will come into force as of July 2017. On other occasions as with the entry into force of the SEPA I have generated my classes in .net from these files.
The problem is that xsd.exe requires that elements be defined for each type in the xsd. You could do it by hand but if there are many classes it is a bit laborious. I recommend you use Xsd2Code . It is an extension for visual studio (2008 or 2010).
Once installed you open the visual studio, add the xsd file to the project, and with the right button you click on it. Select "Run xsd2code Generation", Generate and generate a class with all the defined types.
I hope it serves you.