Join Serial Data Seperated by Newlines?
Simply reverse the steps you took on the sending side.


Create a char array of sufficient size as well as an index variable to keep track of your position within the array. An Arduino String may be more convenient, though they can cause a lot of problems.
In a loop, use available() to wait for incoming chars and add them to the array you've created, using your index variable. 
Keep going in the loop, while checking for that unique character (\n, perhaps) that signals the end of a packet. Add this last byte to the array and then terminate the string with null or \0.


If you want to re-use the array for another packet, simply set the index variable to 0 and continue.