Above you can see the schematic. I recommend to build it on a perf-board or better to etch its own board.

Please note that the L1 coil is made wrapping 4 windings of a 1mm copper wire on a 7mm long support, which will be removed before soldering the coil.

The C3 trimm-capacitor is used to select the transmission frequency, the R7 trimmer is used to modify the volume.

If you want, you may add a 70cm long wire as antenna near the first coil of L1 from the T2-collector side, or even better a ground-plane FM antenna with a shielded coaxial cable.

Be sure to add an heatsink to the 2N2219 transistor (T2), especially if you use an antenna.