When buying a home, you should always have a professional home inspection performed. You need to know exactly what you are getting. You may be able to negotiate with the seller to have them pay for repairs. You might want to include money for repairs or upgrades in your financing package.  Or you might find that the house needs more work than you are prepared to undertake.

Only use a trained, experienced inspector.  You may have a friend or relative who is a contractor and knowledgeable about building, but will they spend 4 hours or more going over every system of the house and give you an in-depth written report?

When I inspect the home, I will look at the systems that make up the building including:

1. Structural elements: foundation & framing ect...
2. Exterior: Condition of paint, siding, and trim, driveways, walks, and patios, decks, and grading.
3. Roofing: Type and condition of roofing, installation details and flashings
4. Electrical system: Open and inspect the main distribution and sub panels, identify wiring methods (Romex, knob-and-tube), test accessible receptacles for proper grounding and polarity, identify improper installation (such as unprotected cables or splices), locate and test ground fault circuit interrupters.  
5. Plumbing system: Test pressure and flow, locate main shut-off (if possible) operate each fixture, inspect for leaks 
6. Insulation and Ventilation: Identify areas where insulation is inadequate and where inadequate ventilation could cause condensation (leading to rot mold) or poor indoor air quality.
7. Interior: Doors, windows, safety issues, floor coverings.
8. Fireplaces: installation, condition and potential fire hazards.