I hAve an avocado tree that was about 4 ft tall but very skinny so I trimmed it down to about 2&half ft. It seemed to be doing fine. New leaves had sprouted out on the sides of the top even. I moved it outside about 2 weeks ago because I know it likes Warmer climate. I know is turning brown from the top about one inch & up from the roots about 5 inches. What did I do?? Or need to do....

It looks to me like it is just forming bark. Have you felt it to see if it's soft. If it is rot it will get mushy, but if firm, I think bark.