I would assume (and you know what they say about assumptions :)) that most of the following is in the ballpark: (if not, please fight my ignorance)
[li]The science to build a nuclear device, whilst obviously a challenging and complex field, is sufficiently public to allow any competent specialist to follow it and understand the necessary mechanisms of the process.[/li][li]The mechanical necessities and complex circuitry required for control devices would not be any more challenging or difficult to create than those for other legitimate uses.[/li][li] This leaves the collection / purchase / theft / creation of weapons grade plutonium (or uranium) for the device, which I presume is generally the main sticking point.[/li][/ul]
So, given the finances and inclination, is the main complexity and difficulty in obtaining a nuclear weapon solely down to acquiring the right core material for use?
I trust a disclaimer is not required to the fact I am not planning on building such a device.