Designing the Monster is possible, but it depends on how close you want to match the “official” stats.
The canon version is the Annihilator.
However –
3025 – Direct Assault
Mass: 100 Tons 49 crits free (Hand actuators removed)
Structure: Standard (10 Tons)
Engine: 200 (8.5 Tons)
Heat Sinks: 11 Heat Sinks (11 Tons, 13 crits)
Gyro 2 Tons
Cockpit 3 Tons
Armour Standard (19.5)
Weaponry: 4 AC/5 (32 Tons, 16 crits), 8 Ammo (8 Tons, 8 crits), 6 Med Laser (6 Tons, 6 crits)
3025 - Artillery
Mass: 100 Tons 51 crits free (Hand and Lower Arm actuators removed)
Structure: Standard (10 Tons)
Engine: 200 (8.5 Tons)
Heat Sinks: 8 Heat Sinks (8 Tons, 10 crits)
Gyro 2 Tons
Cockpit 3 Tons
Armour Standard (19.5)
Weaponry: 2 Thumper Artillery (30 Tons, 30 crits), 4 Ammo (4 Tons, 4 crits), 2 MLsr (2 Tons, 2 crits), 2LL (10 Tons, 4 crits), SRM4+Ammo (3 Tons, 2crits)
Note – Thumper Artillery is dual barrelled
3050 Clan - Gauss
Mass: 100 Tons 49 crits free (Lower Arm actuators removed)
Structure: Endo (5 Tons, 7 crits)
Engine: 200 (8.5 Tons)
Heat Sinks: 10 Heat Sinks (0 Tons, 4 crits)
Gyro 2 Tons
Cockpit 3 Tons
Armour Standard (19.5)
Weaponry: 4 Gauss (48 Tons, 24 crits), 8 Ammo (8 Tons, 8 crits), 6 ERML (6 Tons, 6 crits)
3100 – Kaiju
Chassis Type Fortress, GroundWalker, Hardened Structure
Mass 450 Tons
Size 1 Hex * 3 Levels Quirk (Illegal)
Power System Fusion (17 Tons)
Motive System (12 Tons)
Heat Sinks 70 (70 Tons)
Construction Factor 150 (15 Tons)
Armour (45 Tons)
Environmental Sealing, Power Amplifiers, Cargo (107 Tons)
Crew: 5
Weaponry: Long Tom*4 (120 Tons), Ammo (20 Tons), 6 LPLs, ECM and Comms (8 Tons)
And the usual superheavy versions