It is very difficult to measure Hall effect with available tools at home.
The Hall coefficient of Aluminum, and of metals in general is low (because there are so many conducting carriers; that's partially why semiconductors are used.
The voltage created by the Hall effect measured with a cuboid (i.e. rectangular) conductor depends on the product of current and magnetic field (so it's good to get both high), and inversely on the thickness. It does not depend on the width (or length) of the conductor. The thinnest commonly (home) available metal is household aluminum foil (about 50 um thick), or candy wrapping foil (about 20-25 um thick).
Use a piece as wide as you think you can create a magnetic flux over. Wider than that will reduce the measured signal because the inactive portions of the conductor will 'short out' the Hall voltage. Wide conductors reduce current density and therefore heating/fusing -- this does not affect the Hall measurement.
The length doesn't matter -- use as long as is convenient. It is important to stabilize the system -- use thumbtacks (with plastic heads if possible) to pin the foil to a wooden board or similar.
Clip your voltage measurement probes to the middle of the sheet. An offset doesn't matter.
Likely the Hall voltage you measure will be in the uV range -- this will require a voltmeter or amplifier capable of sensing such low values.
Apply a DC current (with no magnetic field) and measure the voltage. It will be non-zero because there will likely be an offset in the pickup positions. Ensure the voltage stabilizes (if the system heats up, the offset may change). Then apply the magnetic field, being careful to not disturb the physical arrangement. You will likely first notice quite large voltage shifts as the changing magnetic field induces voltages in the measurement loop. This is not the Hall effect. The voltage measured after the system stabilizes is the Hall voltage. Try again with the opposite field direction -- you should measure the opposite polarity change.
If you don't see the opposite polarity change, then likely what you are observing is slight shifts in the position of the (probably magnetic) leads or pickup points. This would be the same polarity, independent of the applied static field.
In practice, the voltage you might observe is likely less than 1 uV and will require a special (lab-grade) meter to observe.