Unfortunately not. It took me quite a while to figure out how to " bypass" the snapping into place so it looks decent, was to make something ( a house ) , the way I didn't want to. Basically you have to either built in a blocky, uneven formation to work around the environment ( building fences ), or adjust the floor of your home you are building so the walls match the length and width and the type of floor.. Also walls have to be all the same, or same height , in order to build a roof and/or second floor the way it supposed to be. For example - a custom built house- Build a wooden floor in a large square, use matching wooden walls to match the circumference of the floor. Use matching wooden ceiling to match the contour of your walls. If you want a second floor, make sure the wooden walls you are building, match the height of the pre fab stair case they give you. Make sure to build a wooden ceiling ( floor ), that matches first floor wooden walls. Build same wooden walls and then find a roof that fits said walls.
It's complicated, and it shouldn't be. It's a mess that is mentioned a lot in the forums and hopefully it will be addressed in a patch. If you are just now building walls, wait until you build shops in your settlement... Your settlers will basically say " F- you" , I'm getting unemployment " . Meaning they will not attend their shops, but instead congregate behind your workshop in a massive circle J==k. You can still buy their goods however.. So I advise you not to build anything behind your Sanctuary workshop.
Also a heads up.. Settlement " issues " panel is broken. It gives you false information about how well your settlement is doing. TO fix, simply fast travel to your settlement/s, then go back to what you are doing. Heads up # 2. Your settlements will be attacked by raiders, and you will receive a small pop up that you will never notice unless you are looking for it. Heads up # 3. Small spoiler, but not really so I'll say it -- you will get a settlement at an airport eventually... Don't leave any companions there.. They get stuck in the walls..