Honestly, the best approach depends on what you’re leveling and how uneven the rooftop really is. If the furniture has adjustable feet, start there. Turn each foot out gradually, check the piece with a small spirit level, and put a rubber or non-marking pad under the feet so the furniture doesn’t slide or scratch the roof surface. For a small bistro table or a couple of chairs, that plus a thin, UV-resistant shim is often enough.
For anything heavier or more permanent, I would not rely on a stack of random shims. Rooftop furniture leveling gets much safer and cleaner when you create a stable, level zone first. The best solution is usually a low-profile floating platform or a set of adjustable pedestals designed for rooftop decks. You set the pedestals to follow the roof’s slope, then add interlocking deck tiles or a small platform on top. That gives you a flat surface without putting point loads on the roof membrane, and it keeps outdoor furniture shims out of the equation.
If you’re using adjustable pedestals, check the manufacturer’s load rating and make sure the base is protected with a suitable mat or pad. Keep the pedestals slightly inward from the furniture’s footprint so the weight is distributed, and avoid lifting one corner too high just to make a table look level. A wobbly table is annoying; a furniture leg punching through a rooftop membrane is a much bigger problem.
Drainage matters as much as leveling. Most rooftops are designed with a slight slope so water can move toward drains, so don’t try to level the entire roof. Level the furniture or the small deck area, and leave the roof’s drainage path alone. Check that your platform or pedestals don’t block drains or trap water. If you’re using outdoor furniture shims, choose hard rubber, composite, or plastic shims that won’t rot, crumble, or stain the surface, and never stack them so high that the furniture becomes unstable.
Wind is the other issue people forget. Urban rooftops can be gusty, so secure lightweight chairs, tables, and planters with straps, weighted bases, or anchoring points where allowed. Keep furniture away from parapet edges, and check your building’s rules before drilling or attaching anything. For a quick fix, use adjustable feet and a single safe shim; for a proper lounge setup on an uneven rooftop surface, a pedestal-based floating deck is the most reliable way to get a level, drainage-friendly, and tidy result.