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I assume you want a synchronous counter - Use the D flip flop excitation table and draw up your circuit excitation table with your present and next states. Use Karnaugh maps to solve for your D value for each flip flop(4 in your case 'coz it's a 4-bit counter).
Here's a solution actually: www.csci.csusb.edu/schubert/tutorials/csci310/f03/dw4bit.pdf
What exactly are your design needs? The reason I ask is you can design a 4-bit asynchronous counter with just four D flip flops. If you have a requirement that states - count from (0000)b to (1100)b and not (1111)b, then you use NAND gates to asynchronously clear inputs of all flip flops once your counter reaches (1100)b. You could make a case for a similar asynch design which would use 4 FFs and 3 logic gates.
Yup, you can design a synchronous four bit even counter. Draw up your state table with your present and next states, use the D-flip flop excitation table and karnaugh maps and extract your D value for each of the flip flops and you have your even counter! I am not sure how many logic gates it will use though, maybe you can reduce it down to three gates...