There are several different ways to draw this design, so check the page about symbols made with letters to see what other designs are possible. The design on this page is more traditional vertical design.
Here’s how to draw the Chi Rho:

Start the design by drawing a rectangle that’s nine times higher than it is wide. 
Turn the top third of the rectangle into a square. The top of the square is thrice the length of the rectangle’s top side.  
Place a mark in the middle of the square’s right side.  
Turn the square into a cluster of nine squares by splitting it in thirds vertically and horizontally.  
Use the squares and the mark made in step 3 to guide your creation of the Rho’s loop.  
Now to position the Chi. To make things easier, let’s call the length of one side of the littler squares one “unit”. Expand the bottom line of the square two units to the left and mark the mid point. This line will help you later, so return your focus to the original square.  
Place one mark one unit below the lower right corner of the larger square, and a second mark three units below that.  
Now add two more marks: the first one goes one half unit below the right side of the center square on the bottom row and the second goes four units below that.  
Mirror the four marks on the other side of the figure, using the line made in step 6 to guide you.  
Connect the marks to finish the design. 