Tutorials are OK if it's a niche area which doesn't have any good textbooks covering it and the tutor is an expert. However, there are a handful of good digital design books which will teach you how to design and build your own CPU. I would get my hands on a good book and work through it.
As for multisim, well if it works then why not learn it and use it for simulation. If, on the other hand you want to realise your CPU in FPGA or silicon, then you might want to learn something like Verilog or VHDL (*). If you want to see CPU designs in Verilog then have a look at some of the links
here. All of the code was written whilst going through the book
Mano, M. Morris, and Kime, Charles R.
Logic and Computer Design Fundamentals. 2nd Edition. Prentice Hall, 2000.
*) Note that you can still simulate designs written with Verilog or VHDL.