Bandwidth of a modulated signal in analog domain If i am using QPSK modulation with data rate 4 Mbps with rolloff factor $0.5$, then the bandwidth will be symbol $\rm rate\times (1 + rolloff\  factor)$. So here it will be $\rm 2\ MHz\times 1.5 = 3\ MHz$
This is baseband data bandwidth.
So should I use analog filter of bandwidth $\rm 3\ MHz$ or should it be more? or should it be more than that?
The analog filter will be more than that such as to minimize further distortion to the passband. The analog filter bandwidth will depend on its purpose (Tx DAC reconstruction, Rx ADC and mixer anti-alias, interference rejection) while the fine passband filtering would be done by the pulse shaping filter in the Tx itself and the matched filter in the Rx, typically both implemented as digital filters.