Amateur radioastronomy: dish suggestions What kind of amateur radioastronomy can any interested citized do with:

a) A 2 m dish antenna.
b) A 2,5 m antenna.
c) A 3 m antenna.
d) A 5 m antenna. 
e) A >5 m &lt;10 m antenna (likely I can not afford this or the previous but I just want to know...).

Of course, space is sometimes a logistic issue for big stuff, but I wondered what kind of objects or sources can someone do with suitable instruments and with aid enough if not an expert. Projects and links would be welcome!
The size of your dish determines two things:

Along with the temperature of your electronics, determines the signal-to-noise ratio of your telescope.
The size of your dish determines the angular resolution you can expect. This has an approximate relationship of $$ R = \lambda / D$$ where $R$ is your angular resolution, $\lambda$ is your wavelength of light and $D$ the width of your aperture (dish).

Instead of talking about dish size lets talk about interesting things to look at and see what the requirements are:
The Sun
The sun is a good source of radio waves in the 10cm wavelength. Since the sun is around half a degree, we would need a dish at least 11.5 meters before you could expect to see the sun as anything more than a point source.
Jupiter
Jupiter has some magnetic field effects that produce radio waves in the 10-100cm wavelength range. Of course Jupiter is 50 arcseconds across, and would need a dish 412 meters in diameter to do any amount of resolution.
Cosmic Microwave Background
The CMB was one of the earliest measurements of radio waves from space. The strongest peak of the CMB is in the 1mm wavelength. However it is very weak. The original investigators cooled their radio detector with liquid helium, and I imagine something similar would be required.
Terrestrial and Man-made sources
There are plenty of man-made radio sources. Airports have a radio wave emitter in the 10cm range for radar. There are plenty of geosynchronous satellites along the equatorial plane that use the X-band in the ~2-5cm range. These by definition have a strong enough signal to be seen from Earth with even a small dish.
Summary
Resolving power is likely out of the reach of an amateur radio astronomer since the dishes have to be either very large, or you must use a much more sophisticated radio interferometry method to achieve any angular resolution. You can however still see things as point sources in the sky if you are so inclined. An excellent example of what is likely accomplished by most people would be this project here.