Having had a 4x6 raised coop and going to walk in style I can say it definitely helps to go a bit bigger.
Adding windows, vents, using deep litter, tending birds while not in the whipping wind or snow is far easier in a walk in style.
I do still have a small raised coop for isolation/hospital...
Great advice already.
Adding to that....deep bedding is extremely difficult in short coops. A walk in would allow for better management of deep bedding.
Not sure if you can manage it with the roofing you have but a 4x8 is just as easy or even easier to build with minimal waste than a 4x6.