Well now that's ridiculous, but if you're confident, click the title and give it a go.

Don't give me, cash me in,

If free they won't buy me, wherein

You'll wait 'till I come home,

Forecast from if I sit or roam,

My drinks collect, an utter sack.

Mostly white and black.

Deary deary, soppy goose, I met you once, though quite obtuse. You asked me questions, halabaloo, all I did was chew!

Riddle Answer - A Cow

Riddle Explanation
don't give me - don't give a cow.

cash me in - a cash cow.

if free they won't buy me - why buy the cow when you can get the milk for free?

wherein you'll wait 'till I come home - until the cows come home.

forecast from if I sit or roam - it is said that if a cow is sitting then it will rain. Though only an old wives tale and most likely untrue, some theories are surprisingly convincing. For instance, one says that cows are more able to detect increasing air moisture and then lie to preserve some dry grass, or lie to protect their stomachs, which are supposedly more sensitive to changes in atmospheric pressure.