You can administer the activities of the LLC, but you may not add value through the provision of goods or services.You can select vendors and materials and oversee work that is done, and of course handle the expense/income transactions on behalf of the LLC.You can purchase materials separate from the labor, but I would caution into turning yourself into a delivery boy and running to the hardware store every day or few days.

I'm new to the whole entrepreneur world and was wondering if that business that I planned on using for an online store could instead be used to write off expenses on my property rehab.

The Bigger Pockets book store if full of great books: https://www.biggerpockets.com/store

He can still store things in basement and has the use of the space. 

And the construction experience has been vital in the rest of my investing.Note:  Get a contractor bid from Home Depot (and other stores).  

The Bigger Pockets book store if full of great books: https://www.biggerpockets.com/store

Even though the big box stores may not carry what you need, many companies that specialize in windows will be able to provide. 

For example, a store, restaurant, manufacturing business, real estate development company.Using margin on a stock purchase."

The Bigger Pockets book store if full of great books: https://www.biggerpockets.com/store

The Bigger Pockets book store if full of great books: https://www.biggerpockets.com/store