Is your garage attached to the house or is it on its own? If it is attached is there living space above the garage? Are you looking to insulate the walls and ceiling? Are you going to drywall the garage? I would suggest using batt insulation, with a vapor barrier. I would then drywall everything. Before you drywall I would make sure that you have all the electrical and anything else that you want in the walls installed.

If you use a black light you can target the urine areas soak in white vinegar leave for ten min wet vacuum as much up as you can mix up a cup of water with a quarter size dawn dish detergant put in spray bottle saturate area but don't soak. Sprinkle baking soda around on the wet area spread likghtly. let sit until everything dries hard this could take up to a day. break up the crusted area with finger tips when dry then vacuum up. it is a bit time consuming but it is all natural and it works like  nothing else!

Cat smell or cat urine smell? 

If it is the latter, I have had success with Nature's Miracle.  If the smell is just the animal, that will diminsh with time and with changing out blinds, flooring, wall coverings, etc. 

Supplies needed: 

hopper gun and compressor (available for rental at home-center stores), paint tray, paint suit and glasses, stepladder , putty knife, paint mixer, paint roller, masking tape, drop cloths, ceiling texture, primer sealer, spackle

Here are the steps you need to take to get the job done: 

1. Fill any dents or imperfections in the ceiling with spackle, and then apply a coat of primer with a roller. Allow the primer to dry at least four hours.

2. While it's drying, mask off the walls and floor with masking tape and tarps, plastic sheets or drop cloths. 

3. Wearing proper protective clothing and goggles, pour some texture mix into a large bucket and mix according to directions. Use a paint-mixer attachment to achieve a nice blend. The mixture is ready when it's the consistency of thick porridge.

4. Fill the hopper with texture mixture and fire up the compressor. Practice spraying on an old board or a large piece of cardboard to get the feel of the machine.

5. Lightly spray the mixture onto the ceiling, and keep moving to avoid oversaturating any area. Use multiple light coats and allow the texture time to dry between coats. If you spray the texture on too thickly, it will drip off the ceiling.

John,

Are you referring to insulating the ceiling of the garage (i.e. cold floors above)?   Will you be dropping the ceiling or are you looking for options with minimal disturbance?