Anyone build model cars, planes, etc. ?

[Lanshark]

My dad just put together a 1:4 V8 model engine. I believe it was a skill level 3. I got it for him for father's day and he's aready done. I know nothing about models but would like to get him another one possibly at a harder skill. Either another engine for a car or maybe a plane, train or ship. Most models I see on Amazon are too simple for him. He's the type that loves to tinker and really can make anything work. Any suggestions as to a site or particular model I can buy and have it shipped to him?