storage leak

Been while since I posted but I have few questions. I have this small storage shed I converted into a grow room only to realize the piece of shit has a leak after I set up grow equipment but luckily I sealed off room with plastic so nothing was damaged. I don't trust the plastic to hold back rain water forever any tips on what i can use that won't effect my grow room and keep it dry? It an outside shed but I moved grow inside until I can fix this problem because I really want use the shed. But don't want do roof re construction.

Tarp would work.

What type of roof? There is roofing tar that will seal that up and will be much more permanent and stable that just putting sheeting or a tarp over it. It goes on with a paint brush, just buy a super cheap paint brush because it will need to be tossed afterwards. This works if you have isolated where the leak is, otherwise you could be "painting" the entire roof.

http://www.homedepot.com/p/Henry-0-90-Gal-208R-Rubber-Wet-Patch-Roof-Cement-HE208R142/100041225?N=5yc1vZarv7

I foamed my roof from the inside and out and I put a heavy duty tarp on top just in case. I put some screws to hold the tarp to the building.

I dont really want to put alot of time and money into fixing the roof.

thanks for feedback, I've located leak. so won't be issue anymore.