I just start to build my own buildings when there's nothing built in a world I downloaded and that helps though I rezone any lots zoned for things I don' plan on adding right away.It just takes some practice to get good at building and it sounds like you've never taken any time to try to build anything.We've all made mistakes in our early attempts at building and learned from those mistakes.I built a house with only a front door and no bakc door in TS1 and somebody missed work and kids missed school because there was no back door.
I've got a world called Logan installed a few monthes ago and it dosen't even have blank lots placed in the world on opening a new game in it though that isn't a problem for me since I started adding blank lots and building on them.