I was wondering if there is a simple way to create a large circle or circular plates. I want to build a MOC of the Hero Factory assembly tower (In LDD first) but most of the pieces that form circles don't give enough clearance for a decently sized CCBS model. I was wondering if there were any bricks or techniques that would help for this specific MOC.
The largest truely round base plates in the LEGO system fit in a 8x8 square. You can build them from two LegoPlate, Round Half 4 x 8 or from four quarters.
For a bigger (and thicker!) base plate there is a Duplo version of the above mentioned base plate, fitting into a 16x16 studs LEGO system square: LegoDuplo, Plate Round Corner 4 x 8 Double
EDIT: For a thicker base, you can use these bricks: Brick, Round Corner 10 x 10 with Slope 33 Edge. They make a base fitting into a 20x20 square.