It needs to not bend, not be bulky, and to have the tools I need.
Pretty straight forward.
I would be interested to hear why you want to design a new multi-tool. How did you land on a multi-tool as what you want to redesign? The only reason why someone would want to design a new version of something that has literally hundreds of versions for sale, is if they think their version is better- so what would make yours better? Nicer case? Lighter? Less expensive?
https://www.crankbrothers.com/products/m19
https://www.crankbrothers.com/products/f15
Tough to improve on these two options. So I start here and go from there with your improvements?
All seriousness- an aluminum case would be nice, like what the f15 uses. it would help reduce rusting on the tool, keep it from opening up when stored in a wedge bag, and take up less room when pulling stuff out then packing the wedge bag.
So there you go- make a case that is form fitting to the tool and light. People like colors- so anodize it and soon you too will swim in coins like Scrooge McDuck.