please help me as i want to make a den for my dog that completely attenuates em waves of phone
I will assume that your target band is 1-3GHz, typical for mobile phones.
The thickness of the shielding you need is related to the skin effect. At 1GHz, the skin thickness is ~2μm for copper and 3μm for aluminium foil. To effectively block the signal (attenuate by ~60dB), you will want the foil to be about 10 times as thick, so you're looking at 30μm for aluminium. 15μm is what you get with standard cooking foil which will somewhat work, but you should aim for thicker varieties.
The maximum size of holes you can accept is related to the wavelength. At 3GHz, the wavelength is about 10cm. Again, to effectively block the signal you will need holes at most about 10 times smaller, about 1 cm.
How much attenuation your dog requires is another question. Probably none at all.