I’m not sure “altar” is the right word in this instance. I assume you mean a prayer corner or some such, or a place to keep icons, bible, breviary, etc.
A more proper term for a dedicated place to pray is, well, “prayer corner”, or a bit more formal, an oratory.
I have a simple oratory I had built in my office/study/cell, a bit inspired by Carthusian practice (though I’m a Benedictine oblate). A simple chair, prie-Dieu, and partition to separate it from the rest of the room, plus a small shelf for my icon of the BVM and Infant Jesus. Decor is simple, crucifix, a couple of candles, and a censer and voilà. It’s where I pray the Liturgy of the Hours. The partition is permanent, but if the space needs to be used for other things you can use a folding room divider.
Here’s what the result looks like:
(
Please Note: This uploaded content is no longer available.)
Here’s a simple folding partition you could use: