Shunt resistor after MOSFET and op amp to amplify voltage
Is this good idea to measure current?

It's an acceptable way to measure current but remember that the current will be pulsed (due to the PWM) and some form of filtering may be required if you want to measure average current. If you want to measure peak current then that requires some form of synchronous measurement but, the basic front end op-amp circuit remains the same. However, I would suggest a couple of things as per this modified diagram: -

The filter capacitor should be used if you want the average current taken by the load: \$C = \frac{1}{2\pi R F_C}\$ where Fc is the cut-off frequency required and R is the red resistor value.

Add an op-amp protection resistor in case your MOSFET went short circuit or the peak voltage exceeded 3.3 volts (shunt going open). It should be in the realm of 10 kΩ.
Make sure your measurement connections to the shunt resistor are very short (blue wires above).
Make sure your op-amp is capable of working with input voltages at 0 volts and that the output from your op-amp can reach close to the 0 volt rail.


Current range is 0.2-1.4 Amp and LM358

With 0.2 amps and an 85 mΩ shunt, the voltage is 17 mV and the expected voltage on the op-amp output is 34 mV - this should be OK with the LM358.