I'm sure everyone here would be able to help you a lot better if you gave us all the background information on your project.
What is the incoming power source?
What output voltages do you want, and what current rating do you want for them? Do you have specific loads that you want to be able to drive? If so, can you describe them?
Multiple output voltages is easy to arrange. You'll need a single pole switch, usually rotary, with one position for each output voltage you want, and a voltage divider for each voltage. The divider may contain a trimpot for exact adjustment, or may just contain two resistors.
All of the voltage dividers are connected across the output voltage, and the centre points (outputs) from the voltage divider are fed to a selector switch, which chooses one of them and passes it to the voltage feedback input on the regulator IC on the board.
If you want an on/off switch at the input, you can combine this with the rotary switch. You'll need a two-pole switch instead of single-pole for this, and an extra position for "OFF".
The output voltage is set by a resistor ratio in the feedback path. The operation of the regulator, and calculation of the output voltage setting resistors, are covered in the data sheet
http://www.ti.com/lit/ds/symlink/lm1577.pdf - please read it thoroughly.
Yes it is probably much easier and cheaper to buy that board and add the switchable output voltage feature, assuming that board is suitable for your project in all other respects. If you describe your project, and link to that board, the kind folks here will be able to help you a lot more.