Cannot find a warehouse and install the flooring and draw some line, put some sportlight, fan, then rent to people to play?

Easier and costing wise is cheaper.

Yes, was thinking that too.

I mean for a medium warehouse at least it can hold 2~4 court badminton court, we just construct a cement slab (if there is existing, then no need to construct) and install flooring. Toilet doesn't cost much too. Parking space only need to park 8~16 cars enough?(most of the warehouse can park at least 5~10 cars right?) Road side also can (got complain from later stage ).

But of course constructing a new building is much more better than renovating existing warehouse. Fits all the requirement.

Right. If we compare the ending, of course constructing a new building is the best way to go.

Does badminton court earn as much as futsal court?

Oh yea, right. Most badminton court are rented out monthly. Either you come or not, the management has received your money. While futsal, they only pay as they play. Didn't know that a futsal court can accommodate 3 badminton court. Not bad.