Here are ALL 12 of the achievements and what needs to be done to get them. They are worth a total of 200 points.
If I Had A Hammer (5)
Build a lumbermill (Single-Player).
Siegfried (or Roy) (5)
Train a Kefling (Single-Player).
Friend (10)
Collect 10 unique player banners from other giants during
Xbox Live play.
Think Big (10)
Build a building made of more than 8 pieces (Single-Player).
World Traveler (10)
Play in an Online game where 20 different player banners appear.
Big Bully (10)
Became the big bully of the village (Single-Player).
Like Rabbits (15)
Reach a total Kefling population of 30 (Single-Player).
Haberdasher (20)
Encounter every possible Kefling hat (Single-Player).
Vanity (20)
Secret.
Frank Lloyd (25)
Unlock 25 blueprints (Single-Player).
Master Builder (25)
Build a cathedral (Single-Player).
King (40)
Finish a complete castle with 3 connected parts (Single-Player).