need help with turbo (compressor/turbine) sizing

Ok I bought a book called Maximum boost that is all about making your own turbo kit for your car. It is a great book , but what i don't get from it is if the hp is directly related to the size of the housing or the size of the compressor/turbine. From what i am getting, the housing is what gives you the hp numbers and the selection of the commpressor/turbine moves where your peak efficiency is and how long it takes to spool. Is this true? Also, are all components universal? Like can i put in a compressor that I want into any housing? Same question for turbine.
Could use all the advice I can get.