If your foundation is not completely level, cut the sill plate slightly or use shims at 1 foot increments to make it level all around. Start laying the sill at highest point if you don’t want to cut the plate. Remember to use pressure treated lumber and lay down a sill gasket or seal. Always square-up exterior walls to the inside edge to account for any slight differences in sawn dimension and have all “bows/crowns” faced to exterior. This will make interior walls as square as possible and exterior finish can more easily hide defects than can be hidden by drywall. Nail a few spacers to outside edge of walls and then tie a string so that spacers can just touch the horizontal string. Move the wall to adjust the spacing and then nail it down. (similar to lining courses of block). When framing walls, don’t install the top of double top plate until after partitions are up. Then install top plate being careful to not have butt joints over another joint, but do butt-join over the middle of a stud. This overlaps the plates and increases the strength. Plus, the top plate of a partition will join the exterior wall with an overlap. To install a 1”X6” let-in brace; lay board diagonally across studs while wall section is on the ground and tack it in place. Cut each stud on both sides of 6” width and then cut ends of board where they cross the leftmost and rightmost studs. Plunge-cut the studs for 1X6 notch. Nail each end of brace in place but leave all other nailing into studs until after the wall is up and plumbed/leveled/squared. Or, use L shaped metal brace by cutting kerf for the small end of L. Do not attach the top plates of interior partitions to the bottom chord of trusses; it could cause the wall to move with expansion/contraction and crack the drywall seams and moldings.