There was an article or two in the RSGB Radio Communications magazine a few years back, using a PIC microprocessor. A lot depends on how much power you are building it for, and what antennas you are going to match. For example, my vertical at 400 watts on 80m needs a tuning capacitor that can hold off 5000 volts!
For highest power, you need a vacuum variable capacitor and (ideally) a good variable inductor. But you can substitute air cored coils and a motor driven switch. You then need to decide on a tuning mechanism...I have linear feedback from positioning potentiometers. The voltage is then digitised and compared with a pre-programmed memory to decide which way to drive the servo motors - the memory has an address input derived from the transceiver frequency.
The usual L network has the problem that the working Q is a function of the impedance transformation ratio, and as the working Q goes up, so do the circulating currents and the losses. This is why all the commercial tuners are somewhat limited in impeadance matching range and power, or they're all pretty big - and most of them still have some limitations. A military 400 watt manual tuner designed to match antennas such as a pair of 16 foot whips at 2 MHz up to a long wire and operate up to 22 MHz, was manually tuned and in a box about 2 foot cube. And it wasn't that size just for fun.....