Website development includes both the front-end and the back-end. So, I assume that you are working upon both the front and back-end.
It mostly depends on the developer. Each developer has a different workflow. I personally prefer to go about the design first. Once all of the required pages are done, I commence working on the back-end. In my opinion nobody enjoys the same level of expertise over design and development. Everybody has their own strength and weakness. Once the most difficult part is taken care of, the remaining part becomes relatively easier.