The 1st pattern B Major scale takes it’s root note positions from the B shape open chord. When looking at the open B chord, the root notes are on the 1st fret B string and the 3rd fret A string.
B
Important: The notes used in the B Major scale are B, C#, D#, E, F#, G#, A#, there are five sharps in the B Major scale.
If we take a look at the scale on the fretboard, you will see something like the following pattern… the root notes are marked with the “X“
| $1.0.$2.X.$6.0 || $3.1.$4.1.$5.1 | $1.2.$2.2.$4.2.$5.X.$6.2 | $3.3 | $1.4.$2.4.$4.4.$5.4.$6.4 |
Note: In the diagram above it’s the fret numbers that are indicated not the scale degrees, and it isn’t the way you would normally write out a scale using TAB, it’s just to illustrate the fingering pattern of the scale. 
When playing this scale on the guitar, I normally start on the lowest pitch root note, the 2nd fret A string with the middle finger, and play up to the highest pitch note of the scale, 1st string 4th fret, which is the G#.
| $5.2 4 $4.1 2 4 $3.1 3 $2.0 2 4 $1.0 2 4 |
Descending back to the lowest pitch note of the scale, the E at the open bottom E string.
| $1.4 2 0 $2.4 2 0 $3.3 1 $4.4 2 1 $5.4 2 1 $6.4 2 0 |
Then back up in pitch to the B root note on the 2nd fret A string.
| $6.0 2 4 $5.1 2 |