You only have to peek at an internet search result to realise that every man and his dog has an opinion about building a workbench. As always these opinions vary from useless to overkill with the sensible answer being somewhere in the middle.
One of the more informative books I found on the matter is WorkBench Design by Christopher Schwarz. He describes a number of design considerations such as the height of the worktop, the overall size and proportions of the bench, the placement of the vice or vices and how to go about making a couple of the included designs. As with all of the references I found, the dream scenario is to have several benches of different sizes and heights in your workshop. Higher benches are often better for close or detail work, lower benches are preferred for planing as you can apply more upper body strength to the task.
One area where opinions do seem to agree is that the bench should be solid and not wobble as you use it. This boils down to making it substantial and heavy, if the top flexes or the legs rack from side to side then it probably won't be much use as a workbench.
The next requirement is help with actually making your bench. Having watched many youtube offerings it quickly becomes apparent that some people are just difficult to listen to. They have good things to say but the presentation is just hard work (this is of course very open to opinion). One youtube series that I did like was by Paul Sellers. He advocates hand tool working and built his example bench in his back garden partly to prove that you don't need many tools or equipment and by definition you probably haven't got a workbench available yet anyway. He has also published a book which includes guidance on making such a bench, the book is in 2 volumes and sometimes the combined volumes book is also available.
I elected to build a bench in this general style but tailored to fit the requirements of my relatively small workshop. My bench is 39" high, 60" long and 22" wide. Paul's design calls for an apron on both the front and the back of the bench to resist racking forces but as I have to store stuff under my bench I decided to not put an apron on the front. To compensate the front leg assemblies have a mortise and tenon joint to the underside of the bench top. So far this has proven to be acceptable.
Essentially you need a heap of heavy and straight timber. My bench is laminated out of 2"x4" pine from the local diy warehouse. You will need about 20x8' lengths and it is at this time that the impending weight of your soon-to-be bench becomes apparent. Sorting through the available timber at the store also makes you realise how bendy, twisted or split such wood can be. Nobody in the store said a word as I rejected several dozen propeller-shaped pieces while searching for enough good ones but I did get some funny looks. Should I have sourced finer wood from a more expensive supplier? Possibly, but the main aim was to turn my new found information into a bench that would serve for the forseeable future.
You will also need to give some thought to a vice or vices. Should they be mounted on the left or right side of the front? Should you include a second vice at one end? Should the vice be flush fitting to the front face of the bench? The choices are considerable but again using the forseeable future process I chose a mid-range vice from Amazon.
I'm not going to give a blow by blow description of how to make such a bench, Paul Sellers' videos cover that far better than I ever could. I will however include some progress photos showing different parts of my build.