I've built 2 AR's, and have been extremely satisfied with them. AR's are extremely easy to build, anyone with decent mechanical skills can do it, if you can assemble a bicycle you can build an AR. "Building" an AR really boils down to assembling the fire control group, installing the parts into the lower receiver and adding the stock, when you get a kit from a good company the upper receiver and top end parts are already assembled.
Here are instructions on how to assemble the lower receiver.
http://www.ar15.com/content/guides/assembly/lower/
Most of the tools needed are ordinary household tools, like a screwdriver and hammer, there are 2 specialized tools I recommend, roll pin punches, they are inexpensive and can be found at Brownells.
To assemble the lower kit the only special tools you need are the roll pin punches from Brownell's, the smaller one for the bolt catch pin and the larger for the trigger guard pin.
http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=5551&title=ROLL+PIN+PUNCHES
3/32 is #3 Roll pin punch (for bolt release pin)
item #230-100-003
#3 Roll Pin Punch $3.75
1/8 is #4 Roll pin punch (for trigger guard pin)
item #230-100-004
#4 Roll Pin Punch $3.83
Small item shipping $3.70
total delivered $11.28
J&T Distributing 20" AR15A2 kit $459.95
http://webcats.net/store/merchant.mv?Screen=PROD&Store_Code=J&Product_Code=C2AAK&Category_Code=K
J&T Distributing 16" Carbine kit $459.95
http://webcats.net/store/merchant.mv?Screen=PROD&Store_Code=J&Product_Code=C1C&Category_Code=K
Stag Arms stripped lower receiver $85, Eagle Firearms is out right now, but he will probably have them back in soon.
http://www.eaglefirearms.net/stag_arms.htm
You will need a few magazines, Eagle Firearms has those also.
http://www.eaglefirearms.net/ar15_magazines.htm
I've done business with all these vendors and highly recommend them!