The most straightforward way to maximize your space is to use the full extent of the game's engine.
However, players use creative "workarounds" to give buildings a taller appearance or add semi-functional extra space. Building Beyond the 4-Floor Limit (Workarounds) The "Half Wall" Fifth Floor
Sims cannot natively route to objects floated into the air via mods unless there is a continuous, valid stairs or elevator mod path. Elevated top floors are best used for visual aesthetics rather than active live-mode gameplay.
TwistedMexi has occasionally released specific scripts targeting the floor limit directly (such as expanding builds to 5 or more stories). If you look for these, always ensure you are downloading the version explicitly updated for the current game patch, as outdated versions will cause your game to crash on launch. Method 2: The Vanilla "No-Mod" Height Trick