Well, to design 12V power supply is easy. You need following components:
Four 1N4001 diodes
LM7812 (LM7805 for 5V) regulator
A transformer must produce an output of 14v - 35v AC with an output current within 100mA to 1A, depending on the power you will need. You will easily get one in store or can buy online.
1000uF - 4700uF capacitor
Two 100nF capacitors
Heatsink if required
Further, you will need the tools to make this power supply.
A thing you can cut Veroboard tracks.
Just follow the circuit and shoulder this all on GPB as per the figure.