A building of the Real Estate Price Register (RCN): address, coordinates, the site's average prices and the flats sold in it with the date, price, price per m², market, kind and parties of each transaction. These are the prices the flats sold for, not developers' asking prices. building_slug is the last part of the address of the building's page with transaction prices on deweloperuch.pl, e.g. 23-marca-79c-sopot — comparables of deweloperuch_estimate_property_value carry one in building_slug; when you have none, ask the user for the link of that page. building_url is that page. Order: the unit with the newest transaction first, each unit's transactions oldest first. Do not average transactions whose classification is not 'regular' (share, enforcement, discount…) with regular sales: they are not ordinary sales at a market price; non_regular_transactions counts them. Limits: buildings with flats only, not houses. Returns at most limit units (default 10); truncated and units_omitted say whether and how many were left out, units_total and transactions_total count the whole building. The newest months are often incomplete (the register lags). include_trend=true adds the mean price per m² of transactions around the building (radius radius_km) in the latest 12 quarters — one more request. Buyers and sellers appear only as a type, never by name. Two kinds of prices must not be mixed: developers' asking prices (deweloperuch_search_investments, deweloperuch_get_investment, deweloperuch_get_offer, deweloperuch_get_market_statistics), RCN transaction prices (deweloperuch_estimate_property_value, deweloperuch_get_transaction_statistics, deweloperuch_rank_locations, deweloperuch_get_building) — what flats actually sold for, from the Real Estate Price Register. deweloperuch.pl is a free community project queried politely (one request at a time, results cached): if a result is an error starting with STOP, stop using the deweloperuch_* tools, retry nothing, look for no workaround and tell the user that market data is temporarily unavailable. Fields ending in _url are pages of deweloperuch.pl: give them to the user as links. Result shape: { building_slug, name? (the address as the register writes it; absent when it gives none — the place is then in city), building_url, city, city_slug, street?, lat, lng, avg_price?, avg_area_m2?, avg_price_per_m2? (the site's averages; a value of 0 or less is omitted), first_transaction_date, last_transaction_date, units_total, transactions_total, non_regular_transactions? (e.g. { share: 1 }), units: [{ floor?, rooms?, area_m2, transactions: [{ date, price, price_per_m2, currency? (absent = PLN), market ('primary' | 'secondary'), classification ('regular' | 'share' | 'bulk' | 'government' | 'enforcement' | 'discount' | 'anomaly_low' | 'anomaly_high'), buyer, seller ('natural_person' | 'legal_person'), share? (only when a share was sold) }] }], units_returned, units_omitted, truncated, hint?, neighbourhood_trend?: { radius_km?, total, returned, truncated, quarters: [{ period, avg_price_per_m2?, transactions? }] }, source } — the list key is units.