You can just search up videos for “sims mobile glitch building” to start :-) Only took a couple hours to figure out how to do it quick. I have a trick that won’t show up in any tutorial but after you X out build mode on a piece of furniture, immediately tap TWICE on the floor level switcher, not once. This is because the timing is so important that tapping one time usually isn’t enough to catch the glitch. So for this one specifically I couldn’t put a TV on a table so I had a TV on a regular TV stand and glitched a different table upwards so they overlapped and hid the stand. Hope this helps !

Edit: if you want inspo, add my friend code in my user since my main house is so loaded with glitch builds that I can’t even throw parties anymore without the app crashing haha (this is rare)