90% of the "build" threads seems to be about stealth, specified as assassin. I really dont see why people need "tips" on how to make one, use common sense and just play the game how you want to and you'll be fine, choose the perks that you'll have the most use of suitable to your style, I didn't have any trouble at all selecting perks as they are very well explained in the game.
Edit: I stuck with the traditional assassin class skills (what's left of it).
Sneak
Lockpick
Archery
One-handed
Alchemy
Light armor
Magic is for pussies. :twirl:
To the OP, the above build is what I'm using also. I've got a mask and ring that +40s sneak, and I've been putting perks in Archery to make it deadly at long range (which it is now). I have advanced lockpicking as well, and have found quite a few rare items using it, esp gems and the occasional large bag of gold. One-handed has been perked with dual wpns, increased speed, etc. Works well, but...
...I have found that my faithful companion Lydia, and my horse, sometimes have difficulty allowing me to sneak in outside environments. Even if I dismount after initially spotting enemies and tell Lydia to wait, there are times when my horse will just wade in to a bunch of NPCs on a suicide run, unless Lydia and I get lucky with kills. It happens rarely, but it does happen. I want to keep Lydia around for the extra loot carrying capacity, but sometimes (especially in dungeons/caves, etc.) she can go after a hidden enemy that I didn't see and make things "challenging."
Overall, though, this build works really well, and Skyrim rocks!