Prism
Explorer
Magic items aren't impossible to calculate for - their quite easy. For example you can add '1' in the hit and damage rows of each build.
I, personally, do not recommend using +X magic items. I just remove the +X part and keep the rest.
Its the randomness that's hard to predict and best leaving out. However I know that if I create a TWF character I am likely to have two magic longswords by high level, a GWF would likely have a single magic weapon and a polearm user might well have none. And often those weapons won't be plussed weapons but things like flame tongues, scimitars of speed, swords of sharpness, intelligent swords and even artifacts. This all assume that we use items and tables from the DMG of course. Custom stuff can be anything.