Welcome to the Forum.
You did not say what type of pistol you want to build a loading stand for and different pistols need stands that are a little or a lot different.
I made one of the stands in this picture for my Colt open top revolvers and the other for my 1858 style Remington.
Both of them being revolvers, the stands could be rather short with the shape of the frame support slightly different.
Because the Cap & Ball revolvers have metal frames and grip straps, the grip doesn't need much if any support.
There is a notch in the lower piece for the heel of the grip to hook into, leaving the barrel and the cylinder pointing straight up.
The stands made for single shot muzzleloading pistols are usually quite a bit taller and the lower area should be shaped to provide support to the grip.
Usually, a single shot pistol has a wooden grip that can crack if just the lowest part of the heel is resting on the wood and supporting the gun during loading so this "grip support" idea is rather important.
Maybe someone else will post a few pictures of the loading stands they have made?