I've never seen a circuit diagram for a basic meter, but I would guess that it probably isn't that complex, although the values you are measuring are very small, so may not be able to use a standard circuit board and components. Having said that, with them being available on Ebay for less that €20, there probably isn't much need.
The simplest type is just a wideband rf amplifier, followed by a simple (diode bridge circuit) ac millivoltmeter. But it would be very difficult to build, as sat I.F. is 1-2Ghz, so you'd need to pay close attention to rf construction techniques.
Why bother? just go www.cpc.co.uk , type in "satellite meter", and you'll see one for £8.95! If your order is for £50 or over, delivery is free too.
For actually finding a satellite, while moving the dish around, a better bet is a sat beeper, at about the same price, or a Digisat Pro which does both + diseqc for £40. See www.myerssat.com/home.php?cat=250 .
The simplest type works as I've said above, an IC rf amp feeds an ac millivoltemter (simple moving coil meter configured as ac milllivoltmeter, that is, in a "diode bridge" circuit, look this up if you don't know it). Operating power for amp is taken from the sat receiver's lnb supply.
But, this is microwave frequncies, so it's striplines, metal cans, etc, such stuff is usually made in factories, with "home construction" it probably wouldn't work at all, unless you're extremely skillful!
Please please please send me the schematics as I am desparate as I can not find a satellite finder meter or buy from the web shop pls pls send me the circuit diagram pls pls pls . my mail email address removed