Ground plane for a buck boost regulator circuit
I disagree with Trevor's advice. In his proposal the secondary high-current loop is crippled by introducing two vias in the switching pass, adding unwanted inductance. It also will introduce current spikes into ground plane, which also has negative effect on overall signal integrity. Follow the recommended layout, even if the feedback loop is somewhat inconvenient to route. 

Regarding the ground, the recommended layout is self-contained and doesn't need ground plane. If there is the plane, the circuit should be grounded in one localized point, just as the recommended layout shows. This will eliminate possibility of high-current ripples going into ground plane. 

ADDITION: If the design can afford the ground layer, and the feedback in bottom layer is a nuisance, I see no reason to extend ground pads nor to the right, nor to the left, and keep one ground, at the center. Then the feedback wire doesn't need to be in a different layer,



In this case all HF ripples will be confined to local loops, and DC returns will go to the common (center) point. This the way how all old modules (VRMs) were done, and I believe this is the best way to have the power clean.