Need help choosing an ar 15 in 223 rem for around 500-700 thanks

Check the gun action sites like gunbroker. If you're looking for a basic ar you should be able to find one for around $700 or a little less.

Has anyone heard of or had any experiences with J&T AR-15s they have there basic platform starting at 598 i thing and then it goes up from there

For your price range the DPMS is going to be tough to beat. I have 2 of them and cannot tell a difference between them and higher priced ARs from the way they shoot.

looking to build my own ar now any thing I should now? are there any brands of upper or lower receivers that wont match up?

All the major companies like DPMS, Rock River and Stag should mate up without a problem. Not so certain about smalller companies but they should, it's part of what makes AR so much fun.

Building your own is fun but will not save you any money unless you can find the pieces at rock bottom prices.
Normally a complete lower runs around $250 to $300 and an upper is $500 and up.

I like this one;

http://www.barrett.net/firearms/rec7

How much does one of those cost i cant find a price

Let me know what you think ?

http://www.impactguns.com/store/BAR-REC7.html


If you buy one, you'll be ready to go !