The latter part of the Holmes Basic rulebook contains an evocative drawing titled "SAMPLE CROSS-SECTION OF LEVELS" (pg 38 of the 1st edition, pg 39 of the 2nd and 3rd editions).
While stocked maps of the dungeon levels are not provided, the original Basic Set provided an obvious solution for novice DMs: use the DUNGEON GEOMORPHS - Set One: Basic Dungeons and MONSTER & TREASURE ASSORTMENT - Set One: Levels One to Three provided in the set (at least for the first few leves). The text immediately above the cross-section even originally said that the "geomorphic dungeon levels provided with this game contain many suggestions and will prove very useful".