Building a bass uke from a Buzzards Field kit is fairly straightforward. You don't need to be a master luthier to do it. After getting the instructions and hardware from the kit, the most important attributes are confidence - and the right donor guitar.
Advice on choosing a donor guitar.
You can convert most child-sized guitars into bass ukuleles. However, to get the best outcome in terms of playability and sound you should try to stick to a few basic principles:
Quarter or half sized guitars make the best donors due to their small scale length and body size. They look more like a ukulele when finished. It is possible to use a three quarter size guitar; however you will be at the limit of string length and string tension at this size, so it is not encouraged. It is not possible to use a full-sized guitar. Specifically, you should look for a scale length (not overall length) of between 17 and 23 inches. For reference, the Afan Bass ukulele has a scale length of 21 inches.
Choose a guitar with classical style tuners (horizontal barrels). It is not usually possible to fit the kit to a western style guitar (vertical tuning barrels).
Most child sized guitars are made from linden, lime or basswood throughout. This wood is suitable and will produce a decent sound, however laminated spruce or beech, mahogany tops or even sold topped instruments give the best tones.
When plugged-in the choice of wood has less effect on the amplified tone, but can have an effect on feed-back at high volume. Again, the better the wood, the better the result.
Don’t use toy guitars – they are not strong enough, are made of very poor quality components and have improperly set up fretboards.
There are literally hundreds of brands to choose from on-line, but beware as they don’t all look as good in the flesh as they do on screen. Car-boot sales and charity shops sometimes offer up good used examples too.
Presently, the list of recommended brands include: Tanglewood; Manuel Rodregez; Jose Ferrer and Lauren.
There are issues with converting a tenor into a bass uke. The main issue is that the width at the fret board is too narrow at the nut. Once the Thundergut strings are in place there is very little space to play. Also the head stock itself isn't ideal - the kit is designed to work with classical head stocks. Finally, the contours of a tenor uke are not sympathetic with the supplied EQ. So all in all, I wouldn't recommend the conversion.