You should be able to modify this build pretty easy the hardest(and usually the most expensive) part of this thing is finding the neck. You could even upgrade and use better quality hardware and a metal sound post instead of that wooden dowel he's got, building instruments like this is a fun little project I've seen quite a few Cigar box guitars and coffee can mandolins/banjos they sound great a look cool.
That's pretty rad! I've been wanting to invest in a banjolele for a while now.
I question my craftsmanship however when it comes to making one of those and having it turn out right. I might just be saving up for a $150 one...as after a lot of trial and error I foresee myself spending about that much on DIY banjo/ukulele supplies, haha.
^^ Well if your gonna spend that much but you still wanna DIY you can order kits or parts from Stewart Macdonald its really easy to put together even if you're not a Luthier
http://www.stewmac.com/shop/Kits/Mandolin_Kits/Campfire_Mandolin_Kit.html?tab=Pictures
this mandolin kit is especially nice and not to expensive for the quality you get.
Here's another place you can order pre-made necks to put on whatever you end up using for the body
http://www.warmoth.com/
The alternative that I particulary approve of is buying a beater at a garage sale and taking off the neck which isn't that hard just takes some gumption and a few tools to steam it off
this video shows one way to do it, you dont have to remove the fret at the body joint but watch a few videos on the subject and it should be easy enough for a newbie with a spatula a clothes iron and some patience.
