First when E shape barre chord becomes A shape barre chord as you move up one string, it'st just really because on B string you miss a half step so you need to move your middle finger one fret to the body (there are 2steps and a half between strings 6&5,5&4,4&3,2&1 ; but only 2 steps between strings 3&2)

[br]It doesn't matter if you start with E shape, C shape, G shape barre chord with root on 6th string, to play the chord of the 4th degree of the major scale of that I chord, just move the whole chord 1 string up (so root on 5th string) and when reaching b string move finger one fret towards bridge.

[br]Remember the major scale formula wwhwwwh (123^4567^8) and that moving from string 6 to 5 there is 2 and a half tone so 1+w+w+h=4

So if your I chord is C shape, G shape, D shape, IV chord voicing will be a bit strange I you want to play it on the same fret. Otherwise just find the IV chord using the formula and find where to play it with an easy voicing. For example if chord I is C shape barre chord with root on 6th string on 2nd fret it is a D chord, IV chord will be G so A shape barre chord with root on 5th String 10th fret, or use any open voicing or use CAGED system...

As a side note, why we use E and A shape barre chords is just because they are easy voicings and E shape barre chord strings 654321 are respectively scale degrees 151(8)351(15) so by moving it to 5th string (and doing A shape barre chord) you are only loosing the 15 scale degree (1st degree 2 octaves higher) which we don't need...