How far are you of max paragon? The last squad member does offer an opportunity for paragon points but that last segment of paragon points is a pain to fill, on my female Shepard run through (just finished it earlier) I didn't fill my bar until the very last mission.
As for sentinel builds, I haven't actually played one yet, that's going to be my next play through but what a lot of people playing the game seem to recommend as a build is:
Heavy Warp
Area overload
few points in cryo as it isn't really needed
Tech Armour evolution is down to preference.
Defender due to the paragon plus health bonus, quick cool down is really handy to.
Seeming Sentinels don't get an ammo power, either warp ammo or armour piercing ammo is recommended as a bonus power.
The nice thing about playing a sentinel though is you can have a really flexible style of game play. If you upgrade your tech armour so the explosion it produces when it's knocked of increases you can play a close combat mele class. Alternatively pick extra protection and your a lot tougher to take out.
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