Your purchase agreement has a spot to either waive or inform the seller that you are conducting a private home inspection.  I don't care if you're in investor, builder, experienced home buyer or first time home buyer, you're going to do a private home inspection before moving forward with your purchase.  It is imperative you have a third party professional that looks for various "things" within your new purchase. 

Let's assume you're not an investor, builder or other.  Here are some things you should look at with your realtor before you have to shell out cash to cover the private inspection. 

1) Roof & windows.  You're not close enough or an expert but you can see major wear marks and dilapidation 

2) Gutters & downspouts.  You probably won't be able to see inside but you're looking for signs of clogging or separation

3) Try to establish the years of install for Furnace, Hot Water Tank & A/C Unit.  Not always easy, but sometimes possible

4) Appliances (assuming they're staying).  Turn them on, figure out roughly how long they've been around

5) Toilets & Faucets (not winterized).  Do they drip, flush, clog, etc.

6) Electrical. Do switches turn things on and off? Is the breaker box actually breakers and not old school fuses?

7) Look up as you walk into or out of rooms.  Look for discoloration, separation, or major areas of damage

8) Paint.  Mostly exterior as you're likely to paint inside anyways, but you're looking for major chipping and peeling.

9) Decks, patios, porches, pavement.  You're looking for large dips and raised areas or large cracks of board splits.

10) Smoke & carbon monoxide detectors.  Smokes should be in every bedroom and main halls.  CO2, at least near bedrooms.  It may not be a requirement, but at least plan on either asking for these things or putting them in yourself.

As long as it's your realtor's 2nd day or longer on the job, they have probably already walked through more houses than you have.  Being a little more realistic, your realtor has seen hundreds if not thousands of homes.  Ask them what they're looking for and why and make sure you never are rushed through the home before you both have a chance to look at the things above and more.