Also be sure to increase your BB coverage on your homeowners insurance. Detached garages aren't covered under your dwelling coverage.
If you can swing a walkway to tie the roof of your garage into the roof of your dwelling, it can be covered under your dwelling coverage.
True....polices main dwelling coverage will not cover what is called a detached structure. However most polices will cover other structures on your property not directly connected to the main home. The coverage is generally 10% of the dwelling coverage. If your rebuilding value of your other structure is greater than this limit most companies will sell you more if you want.
As to attaching the garage to your main home there can be other issues with doing that.