The main frame of the roundhouse would have been made of upright timbers, which were interwoven with coppiced wood - usually hazel, oak, ash or pollarded willow - to make wattle walls. This was then covered with a daub made from clay, soil, straw and animal manure that would weatherproof the house. The roof was constructed from large timbers and densely thatched. All of the domestic life would have occurred within the roundhouse.
A new pair of publications from the Latvian National Culture Centre: a 2017 wall calendar and a planner with photos of authentic replicas of 7th-14th century garb representing all the chiefdoms of Late Iron Age Latvia. This one is Latgallian (not sure of the century). I'm going to try to get some of these for balticsmith.com.
Terra Celtica, Poland. Iron Age Celtic Garb
Pembrokeshire. Interior of the re-created Chieftains Hut, an Iron Age Celtic Roundhouse built on the original foundations ,
Iron Age house at Westhay Reconstruction of an Iron Age house at the Peat Moors Centre, Westhay. The house is based on one found at the nearby Glastonbury Lake Village.