Armed Dragon

The Basic Idea is to rush out armed dragon thunder lvl10 as quickly as possible and keep it alive. So most of the cards in the deck are about either searching for armed dragon cards to start the combo chain, add more cards to your hand in order to utilize his effect, or protect armed dragon from destruction.

Outside of starting with thunder lv3 in your hand, you have a few ways to get the combo started.

Both Tempest and wind channeler will search for lv 3 at a discard cost to help you get started, but be warned that discarding a armed dragon thunder with channeler will NOT activate their graveyard effects as she's not a dragon. However, pairing it with tempest WILL activate their effects which means more searches on top of the search.

Armed Dragon flash will also make this work, as it SS's lvl 3 thunder from the deck. Thus helping you start the level up combo.

Artillery Catapult Turtle is also very useful. By tributing itself for its effect, you can rush out a thunder lvl 5, starting you in the combo from their instead of lvl 3.

 

Armed Dragon Lightning is likely to be your prime protection tool, as its searchable with thunder lv7's effect and recyclable with thunderbolt. If you can draw it, the field spell will basically make your thunder lv 10 and white unbeatable while it is in play, as it negates targets and destroys on your lvl 10 monsters.

 

Now the original Lv10 is here due to armed dragon blitz, as thunder's name becomes the same as the original, blitz can be used to SS the original lv10 at no cost. Which leads you to a top row nuke at the cost of a discard.

 

If you cannot get into thunder lvl 10 for some reason, you have other options.
White is a great option as it can be SS'd if you managed to get decently far into the thunder combo but was stopped or if thunder is destroyed. Since it is paired with white veil, you get a backrow nuke and top row destroy on attack, and it negates any back row effects while it attacks which is great.
While tempest is here mostly to push along the armed dragon engine and even reset it if needed, it can be used as a reliable attacker in a bind , as you special summon it by banishing armed dragons, even from the grave.

Now I have not put my extra deck largely for master duel reasons. as the star of your show is your main deck, you dont NEED specific extra deck cards in your extra deck to make this deck work. The extra deck just needs to be filled to be used for pot of extravagance. However, if you want to build your extra deck specifically for this deck. rank 10 xyz monsters will be your best bet, as that will be on your field the most with thunder lvl 10, normal lvl 10, and white. i personally recommend looking at the superdreadnought cards for this, but as every one is UR in master duel, they can get quite expensive. other possibilities are rank 7 xyz monsters due to tempest, you could stop at thunder lv 7 to put one of those out, aside from that im not sure what situation you'd use any others aside from link monsters.