I'm sure Google had said a while back that they ignore nofollow now (i.e they do follow them and consider them).
Anyway, in terms of link building you'd have to be an idiot to only build dofollow links, it's the equivalent of waving a big red flag at Google saying "I'm building links come and ban me."
Even if nofollow links give no value a natural link profile will contain them.
People who build their own links and don't like to "waste time" building nofollow links because they think they have no value are creating a very distinct footprint.