This gist is all the basic tables that you will need to run a Tumblr copycat,
blogs management, user management and so on.
If you familiar with Ruby you will understand that the first table for example is the type of data that the blogs table would have,integer,string, time or datetime.
By copy pasting the gist bellow and doing only one migration you will have the skeletons of a solid database for your Tumblr Copycat.
Along this procedure you will have to write the connections between the different tables.