I've used the circuit quite a few times. If it is a quality built Ramps board; which I believe yours is, there should be no problems hooking up a heated bed to it. Be aware that the mosfet dedicated to the heatbed does get hot and the board is not overly cooled in the materia101 design.
If you want to add an extra fan to cool the stepper driver and the mosfets there should be and extra 12 volt output just below the fuses on the board.
One problem I've had running a heatbed from this board have been the connector coming from the PSU. Mine was just rated for 10 amps. The heatbed in my case was using 12-13 amps and the connector melded. Luckily smaller heated beds demand less amps. S you might be good.
You have the option of two different inputs. One 12 volt for the hotend and one 24 volt for the bed. I myself am running a prusa i3 with a 200x200mm heatbed on a 30amp actively cooled psu and another i3 on two 12 volt psu's in parallel.
Here is a good review of the RAMPS shield
