I don't (yet) own an aircraft and have gone around this thought process about what type of aircraft several times -
Happy to build, despite the views of some that every one is now too time poor to build
Would need to be trailerable and/or easily storable in say a shipping container or small shed
Engine preference is four stroke for fuel consumption and noise reasons
Despite the popularity of the LSA types, which are very nice flying machines, I wonder if there is a sustainable market for the true 'ultralight' ie the fun recreational vehicle equivalent to the 4wd/jet ski/Harley/quad bike etc. Not sure reinventing the past with uncool looking craft will attract new flyers. These new flyers I think must be the target to generate sales.
Trikes despite their shortcomings seem to be doing very nicely in their niche and definitely have the cool/adventure edge.
Looked at small light and efficient - even down to the sd-1 mini plane, but looking at how short coupled they are must be very pitch sensitive and safety comes to mind. Would get very uncomfortable in rough air. Sonex seem good value for money with good heritage and factory support, for some reason not popular in Oz. Heard that not really a good fit for grass runways, and those little wings struggle to make lift on a hot day esp with the 80hp aerovee
Low wings look nice, easy to refuel, good view in turns etc., but when I shut that bubble canopy on a hot day (which is a lot in QLD) they can be hot and need sunscreen like at the beach.
Strut braced high wings are a lot easier to make strong with a safer pilot space - The plethora of versions of the avid flyer type says something about what a lot of people are looking for.
I'm thinking a modern version of the piper cub type with doors optional would be fun, sort of a three axis trike for 1 + 1 persons.
Construction materials - what ever works best for the particular application. Not keen on too much wood - no good in heat and humidity in QLD and it can't be stored outside or without good ventilation in a small shed/trailer.