How to create extra AST node?

Hi there!
I'm trying to construct AST nodes. Are here any docs about that?
Namely I'd like to put "using" type alias to template somewhere in the middle.

using A = C<int>;

Or if C contains more than 1 arg, then

template<parameters-list-except-first-one> = C<int, parameters-list-except-first-one>;

My approach is to create a right parameters for ActOnAliasDeclaration call. Currently I'm looking at how TypeResult parameter is created, so this is all about correct usage of Declarator and DeclSpec classes, perhaps there are some docs or examples?
Stepan Dyatkovskiy