That wee-bit heap o' leaves an' stibble Has cost thee monie a weary nibble! Now thou's turn'd out, for a' thy trouble, But house or hald, To thole the Winter's sleety dribble, An' cranreuch cauld!
The mouse's nest—now just a little heap of leaves and stubbles ("stibble") of grass and hay—cost that mouse an awful lot of work. Just think of the many weary nibbles she made just to chop up and collect the building materials for that nest.
And now, in spite of all her trouble, the mouse has been "turn'd out," or evicted, from her house and "hald" (property) to face all of winter's sleep and drizzle and frosty cold ("cranreuch"—which is probably the Scottish-est looking word in the whole poem with its hard "cr" and "ch" sounds—means frost. Brr).