Layout and construction methods are not critical. Design can easily be tinkered with to scale up or down, or adjust to your requirements. You can get any voltage or any group of voltages you need. Parts are larger. My transformer is about 1.5 x 1.5 x 2 inches.
Caps are bigger too.
Parts cost may be higher unless you have a good transformer on hand. Regulation is not as good. The core of the 12V inverter consists of Q1, T1, D2, and C3. When Q1 is on, D2 will be reverse biased and current will begin to build in T1. When Q1 turns off, that current will be forced to flow through C3 and D2, which will now be forward biased.