Installing an outdoor inlet for a portable generator
If you want this to look decent, and be safe. You want to have something like this:

Circuit Protection
This setup assumes that the generator provides overcurrent, short-circuit,  overload, and ground-fault protection. Likely via a circuit breaker, and a GFCI receptacle.  If this is not the case, you'll want to provide that protection within your wiring.
If the generator output does not have short-circuit, overcurrent, and overload protection, you'll want to install a circuit breaker somewhere (likely between the inlet and the receptacle). If the generator does not provide ground-fault protection, you'll want to have that somewhere as well (likely via GFCI receptacle, or GFCI circuit breaker).
Shock Hazard Protection
You'll notice in the above diagram, that an inlet is used, and that the female end of the gen. cord plugs into the inlet. To understand why this is important, let's take this example.
The power goes out. You go out and start up the generator. You plug one end of a double male ended cord into the generator, and drag the other end over to the &quot;input receptacle&quot;. As you do so, you touch the exposed prongs at the end of the cord. ZAP! You dead.
If the generator does not accept a male plug connection, you'll want to make up a double female cord. That way you'll plug a female end into the generator, and a female end into the inlet. You don't ever want to have exposed energized parts, as they are a serious shock hazard.
Sizing
Make sure all wiring and devices are sized properly. If you're working with a 20 ampere 125 volt output from the generator. That would mean 20 ampere devices, and at least 12 AWG copper wires.
Grounding
As this setup is basically an extension cord, there's no need to bond it to the electrical system of the house.  The neutral-ground bond on the generator should be left in place.
NEC 702.11 says that the generator has to be grounded to a grounding electrode in accordance with 250.30.
Signage
According to NEC 702.7(C), there should sign near the inlet that reads:

WARNING:
FOR CONNECTION OF A SEPARATELY DERIVED (BONDED NEUTRAL) SYSTEM ONLY