Note to self for future all designs: Figure out exactly how much the entire unit is going to weigh before you build it.
I experienced this when designing a mobile, flatpack coffee shop. It is quite easy to forget about the end weight of a unit when designing with many restriction such as max weight capacity, maximum board size (how small does it pack).
The biggest design challenge for this mobile coffee shop was to make it as light as possible, strong as possible and be able to break it down to pack on roof racks. These three characteristic challenges the designers ability as well as the client pocket depth. It is possible to use very light weight materials but these come at a high price.
The end result was a mobile coffee shop that breaks down to be able to fit into a small van weighing in at 85KG.
