Well, first I had the problem with the stairs, which i fixxed now...

 

Another problem NOW is, that I want to create a custom slab.

Works fine, except that if I place a slab on another one, they won't get to a full slab...

First problem fixxed,

 

Now... well... when I place a slab or a stair next to a block (e.g. grass or dirt), they have "no" lightning, or brightness (whatever)...

in your block use this.setBrightness(.1f); or something close too that.

Fixxed it by using this inside the class:

 

this.setLightOpacity(0);