Before you start building, it is important to know what you want in your van, how much space each element will take, and where you want to put it. I drew some options, however there are many different layout possibilities. For example, you can also have the kitchen at the back. Just take your time figuring out what would be the best for you!
Think about what your priorities are. Do you want to close the space of between the driver and passenger seat and rest of the space? Do you space for a shower/toilet? Do you want a big kitchen because you like to cook? Do you want friends to come over and be able to sit comfortably? Will you have to work / study inside you van? Do you want a big garage to store stuff? Do you need to bring nice clothing that you want to put on hangers? These are all questions you should ask yourself when deciding on your perfect layout.