As with most pulse induction detectors, the Pickini detector uses a single monoloop coil.
The coil inductance should be between 200 and 500 microHenry. Ideally 330 microHenry
The easiest coil to build is a basic round coil

just hit a number of nails in a circular pattern into a plank and wind the coil wire around it. Typically: 20 cm diameter and 27 turns will make a nice and small coil suitable for hunting smaller objects like coins.
Tie the windings even tighter together with a needle and a piece of string.
To improve the elecromagnetic immunity from external noise sources like power lines, RF signals..., the coil can be shielded with aluminum foil or copper tape. Make sure that the shielding is not all around the coil, making a short circuit - leave a gap of a couple of centimeters / 1 inch.

When the coil winding and shielding is finished it can be cast in a two component resin.
A shielded cable, like e.g. a USB cable or STP cat 5/6/7 can be used to attach the coil to the board.

The potted coil compared to the XP GoldmaxxPower coil.

Ø 120 mmround36
Ø 150 mmround31
Ø 175 mmround28
Ø 200 mmround26
Ø 250 mmround22
Ø 300 mmround20
Ø 400 mmround17
Ø 500 mmround15
1m x 1msquare10
1.4m x 1.4msquare8
1.8m x 1.8msquare7