Run some searches for diesel generator here, on google, ebay, etc. There are economical units available.

This is just my opinion and I may be wrong:

The one you build will not work as well as a manufactured genset unless you overcome several technical challenges. The time, effort and money you expend will surpass what a manufactured genset will cost. This is fun to think about, research and talk about, but building it would be the application of misguided energy.

If you want to run a one-man research and development project, proceed. If you want to make electricity from diesel fuel (etc ), buy a genset.

Mercedes diesel as a genset engine

WVO generator powerplant

There are more threads on this topic

Twitch is right. You cannot purchase all of the components required, including fabrication of a suitable base, and the addition of the governor and electrical gear for less than the cost of a ready made genset unless you get some of the stuff for free.