Building skill realy crap at that moment. First of all it very difficult to up, even you is alone builder in your clan. Now you must to build hundreds of cooking furnaces to up skill to 90 points. Second thing: repairing buildings you need already on smelting furnace not at the end of building your cstle.
My suggestion is - include repairing into each building skill after 30 points. Use for repair logical materials: repair furnaces with clay and water, houses with planks and nails, domna and walls with stone and clay ect. My mind was broken when i repair smelting furnace with lether, rope, wood and nails. If building branch needs one more skill it may be deconstruction with conversion some of reusable materials like stone, planks, tile, granite, rope. Clay, mortar, leather, watar, fibers are dissapear.
Last skill in mining branch is useless, i don't know anyone who whant to use finding gold or silver ore. When this skill was part of mining it was much better and logical.
My suggestion is - return this in mining and divide mining: searching all types of ore and mining. Serching ore can located aside of earthwork like forestry skill. Mining can include skill sifting ore to finde some gems, or to improve quality of ore. Sieve must have. Or maby it allow to use ore washing chute to get gems or pure ore, it must be interesting.