Question Summary:
Can I pay a fixed fee for a service which may depend on a variable like the weather eg. pay someone $100 to shovel my driveway for the whole winter season? If it snows less, he benefits but if it snows more, I benefit.

Question Detail:

Can I pay a fixed fee for a service which may depend on a variable like the weather eg. pay someone $100 to shovel my driveway for the whole winter season?  If it snows less, he benefits but if it snows more, I benefit.

Answer :

In the name of Allah, Most Gracious, Most Merciful

Assalaamu `alaykum waRahmatullahi Wabarakatuh
 
It is permissible to pay a fixed fee for a service which may depend on an unpredictable variable such as the weather. However, this fee must be paid for the service of the hired individual and not his time.  
 
(Ahsan ul-Fatawa, 7/ 314-315, Saeed)
  إذا استأجر رجلا ليعمل له عملا اليوم إلى الليل بدرهم صباغة أو خبزا أو غير ذلك فالإجارة فاسدة في قول أبي حنيفة رحمه الله تعالى وفي قولهما يجوز استحسانا ويكون العقد على العمل دون اليوم حتى إذا فرغ منه نصف النهار فله الأجر كاملا وإن لم يفرغ في اليوم فله أن يعمله في الغد...
(الفتاوى العالمكيرية، 4/ 477، العلمية)
 
And Allah knows best
Wassalaamu `alaykum
Ml. Sajid bin Shabbir,
Student Darul Iftaa
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah