just here for my two penneth!
timber built like rodgers which i have seen, are great, and very versatile to work with internally for shelves and storage etc etc, and prior to having all your fixed stuff on the walls, they can be easily insualted and improved to the point of ultra cosy too!
prefabs on the other hand, which i have myself, are a little more awkward for wall mounting stuff, but by no means impossible, but the issue of the leaks is easily sorted so long as your concrete base is good level, float finish helps even more if you can, and you simply sit the panels on a bed of sealant as it goes together, mine has been perfect for many years, even though not float fiinished!
the roof panels have let in the odd drip or two, normally when the wind blows the rain sideways and gets underneath the centre flashing cap, but this has been easily eliminated now with simple foam on the inside, and a bit of extra felt to flash over the outside.
the real bonus for us was the price against a block build which we would have loved to do, but at the size we wanted, was simply unaffordable at the time.
we put a 40x20ft base down and built two 20 x 10 garages plus a 20 x 20 workshop, individually accessed, and have never looked back, it works for us.
we didn't need planning because we were replacing an old asbestos hoop nissen hut built on the same size footings, BUT, in their inifinite stupidity, Newark and Sherwood District Council were adamant on their demands for submission of building regs.
The company we chose to supply us, Nottingham Sectional Buuildings, have been in the game for decades, and never met such a request, so the council had to make do with their iso certificates for the construction of the materials themselves and not the assembly, which isn't covered.
we got there in the end, saved a fortune, and are still pleased with it 10 years on.
it worked well for us, and doesn't look an eyesore either in its rural green surroundings, an added bonus!
good luck with the project mate
ps - johnboy might be able to help you with the costings of a brick build versus others as he is (supposedly!) doing the same thing.