I haven't actually used this but it certainly looks useful and is well presented from the outside. Whatever you want to know and whatever you want to do I'm sure they'll be able to help here.
It's open year round with hours according to the season.
So here's the location on the main drag overlooking the old harbour - grab a pic of the artwork
The WEBSITE is excellent with pages in French, Spanish, English, Italian and German.
On the site there is an info request section with various options. I put in my address, ticked a few boxes, and within two days they sent me a very useful brochure with details of hotels, restaurants, campsites, things to do etc. and also a very good town map with some suggested walks.
Wandering around the town really is a pleasure and especially so as all the main places of interest have these useful plaques (in French and English) which give a brief bit of background and history about that particular location. In fact if you photographed them all you would have your little guidebook.
You'll get the history of the port, information about the churches, background of the main buildings and a few notes regarding local notables.
Here's a few examples -
Roscoff is well-provided with free-to-use public toilets. A couple of them are simple "pissoirs" but most are modern with proper facilities and the ones down by the harbour also offer showers (for the showers you need a token from the Tourist Office which costs 2 Euros).
Favorite thing: If you're staying in self-catering accommodation, or are just generally on the road, there's a perfectly good laundrette in the town centre. Not something I've had to use (as yet) but here it is anyway on Rue A Courbet which is part of the town's main street.