You can square up a wall before raising it by measuring from opposite corners. Assuming that both the top and bottom plates are equal in length, and that both ends are the same, the wall is square when the diagonal measurements are equal. Adjust the wall as necessary, then keep it square with sheathing or with diagonal braces before raising it.
When installing roof shingles, do not nail above the sealant strips or the mid-section of the shingle.
When repairing smaller tears in roof shingles, apply a thin bead of roof cement both under and over the tear, then smooth out the top bead with a putty knife. To camouflage the repair, collect some of the color chips that have washed from the shingles into the rain gutters and sprinkle them over the cement.
Credit problems won't prevent you from obtaining a mortgage, but they will increase the cost. So try to put some time between your problems and your home purchase so you can reestablish good credit. Keep in mind, however, that interest rates, home prices, or both might rise while you work to boost your credit score.