Maybe I should clarify my question.
For the guided method, whatever the outcome of your rolls: it will always be limited by the size of the dice. For example, if you chose Armored Suit as your source, you can never roll an archetype higher than 16.
Now for the constructed method, can you freely pick any archetype, or should you also pick an archetype no higher than 16?
In more general Terms; the rules say to 'simply choose whichever option fits best' - but would you say this means to choose from the options of the dice rolls, or choose completely free?
I hope this makes more sense...