Are you studying multimeter design or do you intend to build a multimeter to save money? If the former, I'd recommend requesting a multimeter manual from one or more of the major multimeter manufacturers, like Simpson, Triplett, etc., and studying it. You would probably find multimeter circuits in the series of circuit books by Rudolph Graf or John Markus. Additionally, long ago Howard Sams, publishers of books on electronics, put out a book on multimeter circuits and applications. Probably also had construction schematics.
Multimeters are quite simple in concept, but complex only due the the multitude of ranges and functions they include. So, once you understand how one range of a function works, you understand all the other ranges because the only difference is the resistor values selected by the range switch.
If the latter (want to construct one), unless you really want the exercise of building one, I would strongly recommend buying a multimeter. While it is conceptually very simple to put together a multimeter with very few ranges, once you try to include a practical number of ranges and functions, cramming all those resistors into a handy enclosure would be very demanding on your patience, skills. and manual dexterity and you will end up with a much less functional package than you can buy. Also, the special switching necessary to get all the ranges and functions in a single rotary switch would be virtually impossible to obtain.
With the modest cost of many hobby grade multimeters available today (at least in the U.S.), you would undoubtedly spend a lot more for all the resistors, switches, a sensitive meter, enclosure, etc.
I recommend saving your creative energies for a project that you can't buy dirt cheap on the market.
For one thing, to get reasonable sensitivity in a multimeter, you generally want a meter movement with not more than 50 microamps full scale sensitivity. It is unusual to find such a sensitive meter in surplus today. A lower sensitivity meter movement will result in a multimeter that might load down the circuit you want to measure.
Have fun.
awright