Growing malting barley is an art in itself. The maltster often contracts to the farmer who has to produce a barley with low protein with a high yield. This is no easy task, the protein needs to 12-13% or lower for North American barley varieties and as low as 10.5% for Continental varieties. This often means the fertilizer (nitrogen) is kept to a minimum to keep the protein down.
Now when you malt the barley, this is where it can get complicated. The grains must sprout, but it can't go to far or you break down too many proteins and your S/T ratios are messed up, plus your yield decreases. Cut the germination too short and the malt is under-modified, the enzymes haven't done their job and the malt doesn't perform well in the mash. When the grain is kilned, you have to have tight temperature control to avoid denaturing the enzymes.
I'm not trying to discourage you, but there is a reason there are separate disciplines for maltsters and brewers. It would be interesting to try at least once, but it will be tough to beat a modern commercial malt. In the end, it's likely the beer will suffer.