"Dogs usually sleep on the floor."
Translation:Canes in pavimento dormire solent.
"Solent" is not an adverb. "Solere" is the verb "to be accustomed to". And when there is a two-verb construction, you need the infinitive followed by the conjugated verb, the exact reverse of English. Now, in English we don't have a single verb that means "to be accustomed to" and we always follow that with a noun or a gerund, but it's the same basic syntax.
He wants to drink ~
They want to drink ~
We want to drink ~
The dogs are used to sleeping on the floor ~
Canes in pavimento dormire solent.
The dog is used to sleeping on the floor ~
Canis in pavimento dormire solet.
I am used to sleeping on the floor ~
In pavimento dormire soleo.
Yes, pavimento is more a tiled floor (according to dictionaries), so I guess it's more in a "domus" or a "templum". (It has probably this connotation, and by extension something that is not always tiled, but is inside a building?)
Humi looks more like a natural soil, a dirt floor for instance, as "humus" makes sense in many languages.
There's also "Solum" to say "ground" (It gave the French "sol", same meaning, and it's cognate with the English "sole" in sole of the foot”, according to Wiktionary).
Solum is given for both "floor pavement" and "ground", so it's maybe a more general noun?
In this sentence, maybe it depends if we intend to say that the dogs usually sleep on the parquet, for instance, or just on the ground, in the house, and outside the house.