***With Custom Engineering and Vigilant Watcher rune, sentries will stay out for 60 seconds)
The main strategy behind this build is to get as many sentries out as possible and keep them out. With standard discipline regen, this build should be able to maintain anywhere from 7-20 sentries at any given time (20 only in extremely ideal situations).
You start the battle by laying 3 sentries, casting preparation (with invigoration) and then place 4 more. Right off the bat, you will have 7 sentries for 1 minute shooting for 140% weapon damage (7 x 20%). You then hit your enemies with entangling shot (crowd control and also increases damage due to Cull the Weak). Your main hatred spender, multishot (with suppression fire for more discipline) should be cast repeatedly at mobs. As multishot hits and you gain more discipline, cast additional sentries. For single target DPS, use elemental arrow (frost for slow synergy and crowd control). If you get in trouble, lay a caltrops and run while your sentries do work.
After 30 seconds, you should be able to cast 3 additional sentries from just your standard discipline regen. This will bring your total sentries to 10 (not counting any multishot sentries you were able to cast). At 45 seconds, you can cast invigoration again allowing you to summon 4 more sentries giving you 14+ sentries for 15 seconds (before your original 7 go away).
I think this could be a fun build if you like kiting and traps. Another positive with this build, is that you can achieve all the skills and runes needed by level 40 (fairly low lvl to achieve for end-game specs). I am not sure if the sentries will attack with your weapon speed or if there is a standard speed; if it is standard, then you obviously would want to go with crossbows for the increased damage. Let me know what you think (I haven't played Beta, so any advice would be appreciated).