Structural issues usually show up as sags, bounces, humps, dips, and leans.
They are caused often by construction errors, improper repairs, rot and other moisture issues, termite damage, and did I mention moisture issues.
In looking for structural issues, check the following:
(1) roofline (for dips and sags) (5) attic (framing size, condition, span)
(2) foundation (for leans, bulges, sags) (6) porches (sags, leans, rot and moisture)
(3) walk through (floors shaking a lot) (7) bath and kitchen (water leak damage)
(4) crawlspace (termites; rot especially at exterior, baths and kitchens; and framing size, condition and span)
Eaves Siding (frame and brick)
Gutters Porches (ceiling, floor, columns, railings, steps)
Drainage Windows (original, replacement, storms–condition and function)
Are you planning to add a bath, closet, or laundry area in your house? Adding a whole new room or rooms? Closing in or adding doorways? Thinking about taking out a wall? Understand the impact on the structure and envelope and on the following items.
Heat and air
Walls and ceilings (condition of surfaces and of paint or covering)
Doors and trim
Built-ins and plumbing fixtures (particularly kitchen and bath)