if you are trying to make ralationship links between post types, the easiest way is to use the great "posts 2 posts" plugin by Scribu : http://wordpress.org/extend/plugins/posts-to-posts/

here is the documentation : https://github.com/scribu/wp-posts-to-posts/wiki

hope that could help.

seb.

if you are trying to make ralationship links between post types, the easiest way is to use the great "posts 2 posts" plugin by Scribu : http://wordpress.org/extend/plugins/posts-to-posts/

here is the documentation : https://github.com/scribu/wp-posts-to-posts/wiki

hope that could help.

seb.

EDIT :

Is there a way to list all the posts created under one custom post type (eg: Blueprints) in the edit screen of another (eg: Buildings) in a checklist (or similar)

yes ! in the edit screen of each post types depending on the associations you create between them. not a checklist, but similar, well, better ! this plugin gives you the ability to add/remove/reorder, with drag and drop, your linked posts/post types/pages and even users if you need...

so that individual bluebrints can be associated with individual buildings?

absolutely ! not only "one to one" relationships inbetween different post types, but also "many to many" and "one to many"... you choose. see the manual.