Difference in Bruhat-Tits Building of $PGL_n$ and $SL_n$

Question

I have a basic question/ clarification required about Bruhat-Tits buildings of the groups of $GL_n$, $PGL_n$ and $SL_n$ over say a finite extension of $\mathbb{Q}_p$. I have seen in different documents the groups $PGL_n$ and $SL_n$ being used interchangeably to define the same Bruhat-Tits building, using lattice chains for example (Can't think of good references off the top of my head, but I can try to have exact references if required). But I have also heard people say that there are subtle differences between these. Can someone explain or point out a reference where the examples of these groups and their differences (if any) are discussed?