Unless it is already heated and cooled, you will need to address heating and cooling as well as insulation. That said, if you are willing to have it be a casual movie room that doesn't have to be permanently changed, make sure the garage door seals well to the floor (pipe insulation works for this), lock the garage door (with the bar thing in the middle), cover the floor with carpet tiles (they have a water-resistant backing), hang dark light blocking drapes on the walls and the garage door, install seating (lounge chairs with cup holders would be an inexpensive and comfy way to go) and a projector and a screen and speakers. Put a table in the corner with a popcorn machine, napkins, and some sort of drink dispenser. Maybe have a large basket somewhere with soft blankets available for use.
Here are a few ideas. You can dye drop cloth materials a dark color and make curtains for the windows. You can paint the walls and purchase tile carpet for the floor. Here is the drop cloth material I recommend and here is an example of carpet tiles. https://amzn.to/2Ght2X2https://amzn.to/2XjwaIG
We've in the process of building a porch onto the front and side of our house (wraparound). We have the porch floor on, and now we're stuck, trying to decide which wo...
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We have a deck that we spent three weekends re-doing with a HGTV recommended deck restoration product that peeled in 9 months. Cleaned and scraped, replaced rotted bo...
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Unless it is already heated and cooled, you will need to address heating and cooling as well as insulation. That said, if you are willing to have it be a casual movie room that doesn't have to be permanently changed, make sure the garage door seals well to the floor (pipe insulation works for this), lock the garage door (with the bar thing in the middle), cover the floor with carpet tiles (they have a water-resistant backing), hang dark light blocking drapes on the walls and the garage door, install seating (lounge chairs with cup holders would be an inexpensive and comfy way to go) and a projector and a screen and speakers. Put a table in the corner with a popcorn machine, napkins, and some sort of drink dispenser. Maybe have a large basket somewhere with soft blankets available for use.
Photos
https://www.google.com/search?q=garage+into+movie+room+cheap&tbm=isch&source=univ&sa=X&ved=2ahUKEwiD-Lzw3NLhAhUKSa0KHYFQCcUQsAR6BAgIEAE&biw=1536&bih=740
Videos
https://www.google.com/search?q=garage+into+movie+room+cheap&source=lnms&tbm=vid&sa=X&ved=0ahUKEwiD-Lzw3NLhAhUKSa0KHYFQCcUQ_AUIECgD&biw=1536&bih=740
Here are a few ideas. You can dye drop cloth materials a dark color and make curtains for the windows. You can paint the walls and purchase tile carpet for the floor. Here is the drop cloth material I recommend and here is an example of carpet tiles. https://amzn.to/2Ght2X2 https://amzn.to/2XjwaIG