Firstly you have to understand what you mean by accuracy.
For a reflector antenna the key figure is RMS error which using the Ruze formula gives a certain Gain Loss.
At 4m the only way to make the reflector is spinning if it is parabolic or stretch forming panels if it is a shaped reflector.
To achieve a 0.1mm gap from the true antenna surface would be tough. With traditional processes the best you could achieve would be a 0.5mm max gap.
Hope this helps.
ScotAllan