I'm building a 6x4x4 doghouse to sit inside a 10x8x8 plastic shed. I have heaters runninng inside the shed on cold days. I do renos on the side and am in 2nd year engineering but unfortunately I've never worked with insulation before. What would the cheapest, easiest solution be here? Is there a specific size of dimensional lumber that would sit flush with insulation? Do I need homewrap?

 Also, there are missing skylights running along the center of the shed roof that have to be covered. I'm using spray foam to fill the internal edges that come apart with time, and for now I've covered the holes with thick rubber mats. What would be a cheap and easy solution for the roof? Ideally I'd like to just cover the whole roof in something, but I have nothing to pin shingles to seeing as it's plastic. Please bare with me I'm 18 and retarded, any help is appreciated.

>>2601344 (OP)

Should have clarified, but it's not worth insulating the entire shed so I'm only looking to insulate the doghouse as I build it.

>>2601344 (OP)

Sorry for the mess of a post, but for reference the doghouse is for a Cane Corso who looks like she'll be around 120lbs fully grown. She doesn't chew on stuff thankfully, and doesn't defecate in her bed.

bubble wrap between 2 layers of thicker mylar foil is probably the cheapest insulation

>>2601344 (OP)

unless you live in Alaska something a like a dogigloo can keep a dog warm all night, and it only has a single plastic wall

Agreed and although DIY is generally a good way to get a better product for the value... Just buy the dog igloo. The round dome shape has better thermal properties and is structurally stronger. You can give the dog a blanket in there if you are really worried about it. With insulation, you would need to finish out the inside walls and that's really unnecessary for a dog house.
