If you absolutely HAVE to make your own, the World Health Organisation has two recipes for sanitising hand-rubs (pre-dating the current coronavirus outbreak) and a lot of stuff about care while making it. It is 60%, but if soap and water are not available nothing else is available it could be better than staying dirty - and possibly proportions could be changed to make it 70%. The amount that their quantities produce is more for a community project, but the principles are made clear, and the reasons for each ingredient. For instance, the hydrogen peroxide mentioned elsewhere is for sterilising any bacteria that may linger in the mix, not as part of the active ingredients .
www.who.int/gpsc/5may/Guide_to_Local_Production.pdf
Quote from WHO page -
“Efficacy
It is the consensus opinion of a WHO expert group that WHO-recommended hand-rub formulations can be used both for hygienic hand antisepsis and for pre-surgical hand preparation.
Hygienic hand-rub
The microbicidal activity of the two WHO-recommended formulations was tested by WHO reference laboratories according to EN standards (EN 1500). Their activity was found to be equivalent to the reference substance (isopropanol 60% v/v) for hygienic hand antisepsis.”