Join Date: Jan 2015
Location: West Palm Beach, FL
Get the existing wood floor out of there. Take a look at the existing subfloor and see if it too needs to be replaced. If not, install your advantech over it. Schlueter wants a nice smooth surface for installation over.
As for cutting your piece, there are three ways to go about it - template (cardboard, door skin, etc), use your existing drawing with an angle finder to locate the angles, or expand on your existing drawing by taking more measurements of diagonals to locate every point.
With option 3 you're basically sketching out a bunch of points on to the new subfloor and then connecting the dots. For instance, starting with the 30 1/8 on the left side of the drawing. Measure from the bottom of the 30 1/8 up to the far side of the 24 3/8. Then on your plywood, swing an arc pivoting off of the bottom of the 30 1/8 marking the arc at your measurement to the top of the 24 3/8. Then swing a second arc pivoting from the top of the 30 1/8 out 24 3/8 and where this arc intersects the first arc, there's your point! Repeat this process around your piece. I normally like to check multiple points and swing multiple arcs to confirm (measure twice, cut once) or at least measure diagonals between various points.
This does look like it would fit on a 4x6 sheet of plywood.