A blogpost by Klaas Pieter Annema is doing the rounds on twitter lately. It appears the builder pattern is quite new to iOS devs since everybody is raving about it. In my own humble opinion I do think it is a bit convoluted for what it's worth.
The followup post by Joris Kluivers makes better use of existing classes: NSURLComponents becomes the builder for an NSURL, and given that these classes are already present and used in other use-cases, the builder pattern makes a lot of sense this way.
But I still feel that rolling just a builder class to construct an object is a bit overkill. But it turns out you don't need two classes: you just need to leverage another feature of Objective-C: protocols.