Question Summary:
Is it permissible to prepare a stage for weddings and parties?

Question Detail:

Is it permissible to prepare a stage for weddings and parties?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
You refer to preparing stages for parties and weddings. Generally, such gatherings are not void of fitna and un-Islamic practices. Therefore, it is inappropriate for a Muslim to attend, let alone contribute, towards such functions. Furthermore, Islam advocates simplicity in every aspect of life including weddings. Consider the following Ahadith

The most blessed marriage is that which is least burdensome[1]
 
 

 
Verily, simplicity is from Iman
In light of the above quoted Ahadith, we advise you to avoid preparing stages for such functions. 
 
And Allah Ta’āla Knows Best
Muntasir Zaman
Student Darul Iftaa
New York, USA
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net